GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc6190

Internet Engineering Task Force (IETF) S. Wenger Request for Comments: 6190 Independent Category: Standards Track Y.-K. Wang ISSN: 2070-1721 Huawei Technologies

                                                            T. Schierl
                                                        Fraunhofer HHI
                                                      A. Eleftheriadis
                                                                 Vidyo
                                                              May 2011
            RTP Payload Format for Scalable Video Coding

Abstract

 This memo describes an RTP payload format for Scalable Video Coding
 (SVC) as defined in Annex G of ITU-T Recommendation H.264, which is
 technically identical to Amendment 3 of ISO/IEC International
 Standard 14496-10.  The RTP payload format allows for packetization
 of one or more Network Abstraction Layer (NAL) units in each RTP
 packet payload, as well as fragmentation of a NAL unit in multiple
 RTP packets.  Furthermore, it supports transmission of an SVC stream
 over a single as well as multiple RTP sessions.  The payload format
 defines a new media subtype name "H264-SVC", but is still backward
 compatible to RFC 6184 since the base layer, when encapsulated in its
 own RTP stream, must use the H.264 media subtype name ("H264") and
 the packetization method specified in RFC 6184.  The payload format
 has wide applicability in videoconferencing, Internet video
 streaming, and high-bitrate entertainment-quality video, among
 others.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6190.

Wenger, et al. Standards Track [Page 1] RFC 6190 RTP Payload Format for SVC May 2011

Copyright Notice

 Copyright (c) 2011 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Wenger, et al. Standards Track [Page 2] RFC 6190 RTP Payload Format for SVC May 2011

Table of Contents

 1. Introduction ....................................................5
    1.1. The SVC Codec ..............................................6
         1.1.1. Overview ............................................6
         1.1.2. Parameter Sets ......................................8
         1.1.3. NAL Unit Header .....................................9
    1.2. Overview of the Payload Format ............................12
         1.2.1. Design Principles ..................................12
         1.2.2. Transmission Modes and Packetization Modes .........13
         1.2.3. New Payload Structures .............................15
 2. Conventions ....................................................16
 3. Definitions and Abbreviations ..................................16
    3.1. Definitions ...............................................16
         3.1.1. Definitions from the SVC Specification .............16
         3.1.2. Definitions Specific to This Memo ..................18
    3.2. Abbreviations .............................................22
 4. RTP Payload Format .............................................23
    4.1. RTP Header Usage ..........................................23
    4.2. NAL Unit Extension and Header Usage .......................23
         4.2.1. NAL Unit Extension .................................23
         4.2.2. NAL Unit Header Usage ..............................24
    4.3. Payload Structures ........................................25
    4.4. Transmission Modes ........................................28
    4.5. Packetization Modes .......................................28
         4.5.1. Packetization Modes for Single-Session
                Transmission .......................................28
         4.5.2. Packetization Modes for Multi-Session
                Transmission .......................................29
    4.6. Single NAL Unit Packets ...................................32
    4.7. Aggregation Packets .......................................33
         4.7.1. Non-Interleaved Multi-Time Aggregation
                Packets (NI-MTAPs) .................................33
    4.8. Fragmentation Units (FUs) .................................35
    4.9. Payload Content Scalability Information (PACSI) NAL Unit ..35
    4.10. Empty NAL unit ...........................................43
    4.11. Decoding Order Number (DON) ..............................43
         4.11.1. Cross-Session DON (CS-DON) for
                 Multi-Session Transmission ........................43
 5. Packetization Rules ............................................45
    5.1. Packetization Rules for Single-Session Transmission .......45
    5.2. Packetization Rules for Multi-Session Transmission ........46
         5.2.1. NI-T/NI-TC Packetization Rules .....................47
         5.2.2. NI-C/NI-TC Packetization Rules .....................49
         5.2.3. I-C Packetization Rules ............................50
         5.2.4. Packetization Rules for Non-VCL NAL Units ..........50
         5.2.5. Packetization Rules for Prefix NAL Units ...........51

Wenger, et al. Standards Track [Page 3] RFC 6190 RTP Payload Format for SVC May 2011

 6. De-Packetization Process .......................................51
    6.1. De-Packetization Process for Single-Session Transmission ..51
    6.2. De-Packetization Process for Multi-Session Transmission ...51
         6.2.1. Decoding Order Recovery for the NI-T and
                NI-TC Modes ........................................52
                6.2.1.1. Informative Algorithm for NI-T
                         Decoding Order Recovery within
                         an Access Unit ............................55
         6.2.2. Decoding Order Recovery for the NI-C,
                NI-TC, and I-C Modes ...............................57
 7. Payload Format Parameters ......................................59
    7.1. Media Type Registration ...................................60
    7.2. SDP Parameters ............................................75
         7.2.1. Mapping of Payload Type Parameters to SDP ..........75
         7.2.2. Usage with the SDP Offer/Answer Model ..............76
         7.2.3. Dependency Signaling in Multi-Session
                Transmission .......................................84
         7.2.4. Usage in Declarative Session Descriptions ..........85
    7.3. Examples ..................................................86
         7.3.1. Example for Offering a Single SVC Session ..........86
         7.3.2. Example for Offering a Single SVC Session Using
                scalable-layer-id ..................................87
         7.3.3. Example for Offering Multiple Sessions in MST ......87
         7.3.4. Example for Offering Multiple Sessions in
                MST Including Operation with Answerer Using
                scalable-layer-id ..................................89
         7.3.5. Example for Negotiating an SVC Stream with
                a Constrained Base Layer in SST ....................90
    7.4. Parameter Set Considerations ..............................91
 8. Security Considerations ........................................91
 9. Congestion Control .............................................92
 10. IANA Considerations ...........................................93
 11. Informative Appendix: Application Examples ....................93
    11.1. Introduction .............................................93
    11.2. Layered Multicast ........................................93
    11.3. Streaming ................................................94
    11.4. Videoconferencing (Unicast to MANE, Unicast to
          Endpoints) ...............................................95
    11.5. Mobile TV (Multicast to MANE, Unicast to Endpoint) .......96
 12. Acknowledgements ..............................................97
 13. References ....................................................97
    13.1. Normative References .....................................97
    13.2. Informative References ...................................98

Wenger, et al. Standards Track [Page 4] RFC 6190 RTP Payload Format for SVC May 2011

1. Introduction

 This memo specifies an RTP [RFC3550] payload format for the Scalable
 Video Coding (SVC) extension of the H.264/AVC video coding standard.
 SVC is specified in Amendment 3 to ISO/IEC 14496 Part 10
 [ISO/IEC14496-10] and equivalently in Annex G of ITU-T Rec. H.264
 [H.264].  In this memo, unless explicitly stated otherwise,
 "H.264/AVC" refers to the specification of [H.264] excluding Annex G.
 SVC covers the entire application range of H.264/AVC, from low-
 bitrate mobile applications, to High-Definition Television (HDTV)
 broadcasting, and even Digital Cinema that requires nearly lossless
 coding and hundreds of megabits per second.  The scalability features
 that SVC adds to H.264/AVC enable several system-level
 functionalities related to the ability of a system to adapt the
 signal to different system conditions with no or minimal processing.
 The adaptation relates both to the capabilities of potentially
 heterogeneous receivers (differing in screen resolution, processing
 speed, etc.), and to differing or time-varying network conditions.
 The adaptation can be performed at the source, the destination, or in
 intermediate media-aware network elements (MANEs).  The payload
 format specified in this memo exposes these system-level
 functionalities so that system designers can take direct advantage of
 these features.
    Informative note: Since SVC streams contain, by design, a sub-
    stream that is compliant with H.264/AVC, it is trivial for a MANE
    to filter the stream so that all SVC-specific information is
    removed.  This memo, in fact, defines a media type parameter
    (sprop-avc-ready, Section 7.2) that indicates whether or not the
    stream can be converted to one compliant with [RFC6184] by
    eliminating RTP packets, and rewriting RTP Control Protocol (RTCP)
    to match the changes to the RTP packet stream as specified in
    Section 7 of [RFC3550].
 This memo defines two basic modes for transmission of SVC data,
 single-session transmission (SST) and multi-session transmission
 (MST).  In SST, a single RTP session is used for the transmission of
 all scalability layers comprising an SVC bitstream; in MST, the
 scalability layers are transported on different RTP sessions.  In
 SST, packetization is a straightforward extension of [RFC6184].  For
 MST, four different modes are defined in this memo.  They differ on
 whether or not they allow interleaving, i.e., transmitting Network
 Abstraction Layer (NAL) units in an order different than the decoding
 order, and by the technique used to effect inter-session NAL unit
 decoding order recovery.  Decoding order recovery is performed using
 either inter-session timestamp alignment [RFC3550] or cross-session
 decoding order numbers (CS-DONs).  One of the MST modes supports both

Wenger, et al. Standards Track [Page 5] RFC 6190 RTP Payload Format for SVC May 2011

 decoding order recovery techniques, so that receivers can select
 their preferred technique.  More details can be found in Section
 1.2.2.
 This memo further defines three new NAL unit types.  The first type
 is the payload content scalability information (PACSI) NAL unit,
 which is used to provide an informative summary of the scalability
 information of the data contained in an RTP packet, as well as
 ancillary data (e.g., CS-DON values).  The second and third new NAL
 unit types are the empty NAL unit and the non-interleaved multi-time
 aggregation packet (NI-MTAP) NAL unit.  The empty NAL unit is used to
 ensure inter-session timestamp alignment required for decoding order
 recovery in MST.  The NI-MTAP is used as a new payload structure
 allowing the grouping of NAL units of different time instances in
 decoding order.  More details about the new packet structures can be
 found in Section 1.2.3.
 This memo also defines the signaling support for SVC transport over
 RTP, including a new media subtype name (H264-SVC).
 A non-normative overview of the SVC codec and the payload is given in
 the remainder of this section.

1.1. The SVC Codec

1.1.1. Overview

 SVC defines a coded video representation in which a given bitstream
 offers representations of the source material at different levels of
 fidelity (hence the term "scalable").  Scalable video coding
 bitstreams, or scalable bitstreams, are constructed in a pyramidal
 fashion: the coding process creates bitstream components that improve
 the fidelity of hierarchically lower components.
 The fidelity dimensions offered by SVC are spatial (picture size),
 quality (or Signal-to-Noise Ratio (SNR)), and temporal (pictures per
 second).  Bitstream components associated with a given level of
 spatial, quality, and temporal fidelity are identified using
 corresponding parameters in the bitstream: dependency_id, quality_id,
 and temporal_id (see also Section 1.1.3).  The fidelity identifiers
 have integer values, where higher values designate components that
 are higher in the hierarchy.  It is noted that SVC offers significant
 flexibility in terms of how an encoder may choose to structure the
 dependencies between the various components.  Decoding of a
 particular component requires the availability of all the components
 it depends upon, either directly, or indirectly.  An operation point

Wenger, et al. Standards Track [Page 6] RFC 6190 RTP Payload Format for SVC May 2011

 of an SVC bitstream consists of the bitstream components required to
 be able to decode a particular dependency_id, quality_id, and
 temporal_id combination.
 The term "layer" is used in various contexts in this memo.  For
 example, in the terms "Video Coding Layer" and "Network Abstraction
 Layer" it refers to conceptual organization levels.  When referring
 to bitstream syntax elements such as block layer or macroblock layer,
 it refers to hierarchical bitstream structure levels.  When used in
 the context of bitstream scalability, e.g., "AVC base layer", it
 refers to a level of representation fidelity of the source signal
 with a specific set of NAL units included.  The correct
 interpretation is supported by providing the appropriate context.
 SVC maintains the bitstream organization introduced in H.264/AVC.
 Specifically, all bitstream components are encapsulated in Network
 Abstraction Layer (NAL) units, which are organized as Access Units
 (AUs).  An AU is associated with a single sampling instance in time.
 A subset of the NAL unit types correspond to the Video Coding Layer
 (VCL), and contain the coded picture data associated with the source
 content.  Non-VCL NAL units carry ancillary data that may be
 necessary for decoding (e.g., parameter sets as explained below) or
 that facilitate certain system operations but are not needed by the
 decoding process itself.  Coded picture data at the various fidelity
 dimensions are organized in slices.  Within one AU, a coded picture
 of an operation point consists of all the coded slices required for
 decoding up to the particular combination of dependency_id and
 quality_id values at the time instance corresponding to the AU.
 It is noted that the concept of temporal scalability is already
 present in H.264/AVC, as profiles defined in Annex A of [H.264]
 already support it.  Specifically, in H.264/AVC, the concept of sub-
 sequences has been introduced to allow optional use of temporal
 layers through Supplemental Enhancement Information (SEI) messages.
 SVC extends this approach by exposing the temporal scalability
 information using the temporal_id parameter, alongside (and unified
 with) the dependency_id and quality_id values that are used for
 spatial and quality scalability, respectively.  For coded picture
 data defined in Annex G of [H.264], this is accomplished by using a
 new type of NAL unit, namely, coded slice in scalable extension NAL
 unit (type 20), where the fidelity parameters are part of its header.
 For coded picture data that follow H.264/AVC, and to ensure
 compatibility with existing H.264/AVC decoders, another new type of
 NAL unit, namely, prefix NAL unit (type 14), has been defined to
 carry this header information.  SVC additionally specifies a third
 new type of NAL unit, namely, subset sequence parameter set NAL unit
 (type 15), to contain sequence parameter set information for quality
 and spatial enhancement layers.  All these three newly specified NAL

Wenger, et al. Standards Track [Page 7] RFC 6190 RTP Payload Format for SVC May 2011

 unit types (14, 15, and 20) are among those reserved in H.264/AVC and
 are to be ignored by decoders conforming to one or more of the
 profiles specified in Annex A of [H.264].
 Within an AU, the VCL NAL units associated with a given dependency_id
 and quality_id are referred to as a "layer representation".  The
 layer representation corresponding to the lowest values of
 dependency_id and quality_id (i.e., zero for both) is compliant by
 design to H.264/AVC.  The set of VCL and associated non-VCL NAL units
 across all AUs in a bitstream associated with a particular
 combination of values of dependency_id and quality_id, and regardless
 of the value of temporal_id, is conceptually a scalable layer.  For
 backward compatibility with H.264/AVC, it is important to
 differentiate, however, whether or not SVC-specific NAL units are
 present in a given bitstream.  This is particularly important for the
 lowest fidelity values in terms of dependency_id and quality_id (zero
 for both), as the corresponding VCL data are compliant with
 H.264/AVC, and may or may not be accompanied by associated prefix NAL
 units.  This memo therefore uses the term "AVC base layer" to
 designate the layer that does not contain SVC-specific NAL units, and
 "SVC base layer" to designate the same layer but with the addition of
 the associated SVC prefix NAL units.  Note that the SVC specification
 uses the term "base layer" for what in this memo will be referred to
 as "AVC base layer".  Similarly, it is also important to be able to
 differentiate, within a layer, the temporal fidelity components it
 contains.  This memo uses the term "T0" to indicate, within a
 particular layer, the subset that contains the NAL units associated
 with temporal_id equal to 0.
 SNR scalability in SVC is offered in two different ways.  In what is
 called coarse-grain scalability (CGS), scalability is provided by
 including or excluding a complete layer when decoding a particular
 bitstream.  In contrast, in medium-grain scalability (MGS),
 scalability is provided by selectively omitting the decoding of
 specific NAL units belonging to MGS layers.  The selection of the NAL
 units to omit can be based on fixed-length fields present in the NAL
 unit header (see also Sections 1.1.3 and 4.2).

1.1.2. Parameter Sets

 SVC maintains the parameter sets concept in H.264/AVC and introduces
 a new type of sequence parameter set, referred to as the subset
 sequence parameter set [H.264].  Subset sequence parameter sets have
 NAL unit type equal to 15, which is different from the NAL unit type
 value (7) of sequence parameter sets.  VCL NAL units of NAL unit type
 1 to 5 must only (indirectly) refer to sequence parameter sets, while
 VCL NAL units of NAL unit type 20 must only (indirectly) refer to
 subset sequence parameter sets.  The references are indirect because

Wenger, et al. Standards Track [Page 8] RFC 6190 RTP Payload Format for SVC May 2011

 VCL NAL units refer to picture parameter sets (in their slice
 header), which in turn refer to regular or subset sequence parameter
 sets.  Subset sequence parameter sets use a separate identifier value
 space than sequence parameter sets.
 In SVC, coded picture data from different layers may use the same or
 different sequence and picture parameter sets.  Let the variable DQId
 be equal to dependency_id * 16 + quality_id.  At any time instant
 during the decoding process there is one active sequence parameter
 set for the layer representation with the highest value of DQId and
 one or more active layer SVC sequence parameter set(s) for layer
 representations with lower values of DQId.  The active sequence
 parameter set or an active layer SVC sequence parameter set remains
 unchanged throughout a coded video sequence in the scalable layer in
 which the active sequence parameter set or active layer SVC sequence
 parameter set is referred to.  This means that the referred sequence
 parameter set or subset sequence parameter set can only change at
 instantaneous decoding refresh (IDR) access units for any layer.  At
 any time instant during the decoding process there may be one active
 picture parameter set (for the layer representation with the highest
 value of DQId) and one or more active layer picture parameter set(s)
 (for layer representations with lower values of DQId).  The active
 picture parameter set or an active layer picture parameter set
 remains unchanged throughout a layer representation in which the
 active picture parameter set or active layer picture parameter set is
 referred to, but may change from one AU to the next.

1.1.3. NAL Unit Header

 SVC extends the one-byte H.264/AVC NAL unit header by three
 additional octets for NAL units of types 14 and 20.  The header
 indicates the type of the NAL unit, the (potential) presence of bit
 errors or syntax violations in the NAL unit payload, information
 regarding the relative importance of the NAL unit for the decoding
 process, the layer identification information, and other fields as
 discussed below.
 The syntax and semantics of the NAL unit header are specified in
 [H.264], but the essential properties of the NAL unit header are
 summarized below for convenience.
 The first byte of the NAL unit header has the following format (the
 bit fields are the same as defined for the one-byte H.264/AVC NAL
 unit header, while the semantics of some fields have changed
 slightly, in a backward-compatible way):

Wenger, et al. Standards Track [Page 9] RFC 6190 RTP Payload Format for SVC May 2011

       +---------------+
       |0|1|2|3|4|5|6|7|
       +-+-+-+-+-+-+-+-+
       |F|NRI|  Type   |
       +---------------+
 The semantics of the components of the NAL unit type octet, as
 specified in [H.264], are described briefly below.  In addition to
 the name and size of each field, the corresponding syntax element
 name in [H.264] is also provided.
 F:    1 bit
       forbidden_zero_bit.  H.264/AVC declares a value of 1 as a
       syntax violation.
 NRI:  2 bits
       nal_ref_idc.  A value of "00" (in binary form) indicates that
       the content of the NAL unit is not used to reconstruct
       reference pictures for future prediction.  Such NAL units can
       be discarded without risking the integrity of the reference
       pictures in the same layer.  A value greater than "00"
       indicates that the decoding of the NAL unit is required to
       maintain the integrity of reference pictures in the same layer
       or that the NAL unit contains parameter sets.
 Type: 5 bits
       nal_unit_type.  This component specifies the NAL unit type as
       defined in Table 7-1 of [H.264], and later within this memo.
       For a reference of all currently defined NAL unit types and
       their semantics, please refer to Section 7.4.1 in [H.264].
       In H.264/AVC, NAL unit types 14, 15, and 20 are reserved for
       future extensions.  SVC uses these three NAL unit types as
       follows: NAL unit type 14 is used for prefix NAL unit, NAL unit
       type 15 is used for subset sequence parameter set, and NAL unit
       type 20 is used for coded slice in scalable extension (see
       Section 7.4.1 in [H.264]).  NAL unit types 14 and 20 indicate
       the presence of three additional octets in the NAL unit header,
       as shown below.
          +---------------+---------------+---------------+
          |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |R|I|   PRID    |N| DID |  QID  | TID |U|D|O| RR|
          +---------------+---------------+---------------+

Wenger, et al. Standards Track [Page 10] RFC 6190 RTP Payload Format for SVC May 2011

 R:    1 bit
       reserved_one_bit.  Reserved bit for future extension.  R must
       be equal to 1.  The value of R must be ignored by decoders.
 I:    1 bit
       idr_flag.  This component specifies whether the layer
       representation is an instantaneous decoding refresh (IDR) layer
       representation (when equal to 1) or not (when equal to 0).
 PRID: 6 bits
       priority_id.  This flag specifies a priority identifier for the
       NAL unit.  A lower value of PRID indicates a higher priority.
 N:    1 bit
       no_inter_layer_pred_flag.  This flag specifies, when present in
       a coded slice NAL unit, whether inter-layer prediction may be
       used for decoding the coded slice (when equal to 1) or not
       (when equal to 0).
 DID:  3 bits
       dependency_id.  This component indicates the inter-layer coding
       dependency level of a layer representation.  At any access
       unit, a layer representation with a given dependency_id may be
       used for inter-layer prediction for coding of a layer
       representation with a higher dependency_id, while a layer
       representation with a given dependency_id shall not be used for
       inter-layer prediction for coding of a layer representation
       with a lower dependency_id.
 QID:  4 bits
       quality_id.  This component indicates the quality level of an
       MGS layer representation.  At any access unit and for identical
       dependency_id values, a layer representation with quality_id
       equal to ql uses a layer representation with quality_id equal
       to ql-1 for inter-layer prediction.
 TID:  3 bits
       temporal_id.  This component indicates the temporal level of a
       layer representation.  The temporal_id is associated with the
       frame rate, with lower values of _temporal_id corresponding to
       lower frame rates.  A layer representation at a given
       temporal_id typically depends on layer representations with
       lower temporal_id values, but it never depends on layer
       representations with higher temporal_id values.

Wenger, et al. Standards Track [Page 11] RFC 6190 RTP Payload Format for SVC May 2011

 U:    1 bit
       use_ref_base_pic_flag.  A value of 1 indicates that only
       reference base pictures are used during the inter prediction
       process.  A value of 0 indicates that the reference base
       pictures are not used during the inter prediction process.
 D:    1 bit
       discardable_flag.  A value of 1 indicates that the current NAL
       unit is not used for decoding NAL units with values of
       dependency_id higher than the one of the current NAL unit, in
       the current and all subsequent access units.  Such NAL units
       can be discarded without risking the integrity of layers with
       higher dependency_id values.  discardable_flag equal to 0
       indicates that the decoding of the NAL unit is required to
       maintain the integrity of layers with higher dependency_id.
 O:    1 bit
       output_flag: Affects the decoded picture output process as
       defined in Annex C of [H.264].
 RR:   2 bits
       reserved_three_2bits.  Reserved bits for future extension.  RR
       MUST be equal to "11" (in binary form).  The value of RR must
       be ignored by decoders.
 This memo extends the semantics of F, NRI, I, PRID, DID, QID, TID, U,
 and D per Annex G of [H.264] as described in Section 4.2.

1.2. Overview of the Payload Format

 Similar to [RFC6184], this payload format can only be used to carry
 the raw NAL unit stream over RTP and not the bytestream format
 specified in Annex B of [H.264].
 The design principles, transmission modes, and packetization modes as
 well as new payload structures are summarized in this section.  It is
 assumed that the reader is familiar with the terminology and concepts
 defined in [RFC6184].

1.2.1. Design Principles

 The following design principles have been observed for this payload
 format:
 o  Backward compatibility with [RFC6184] wherever possible.

Wenger, et al. Standards Track [Page 12] RFC 6190 RTP Payload Format for SVC May 2011

 o  The SVC base layer or any H.264/AVC compatible subset of the SVC
    base layer, when transmitted in its own RTP stream, must be
    encapsulated using [RFC6184].  This ensures that such an RTP
    stream can be understood by [RFC6184] receivers.
 o  Media-aware network elements (MANEs) as defined in [RFC6184] are
    signaling-aware, rely on signaling information, and have state.
 o  MANEs can aggregate multiple RTP streams, possibly from multiple
    RTP sessions.
 o  MANEs can perform media-aware stream thinning (selective
    elimination of packets or portions thereof).  By using the payload
    header information identifying layers within an RTP session, MANEs
    are able to remove packets or portions thereof from the incoming
    RTP packet stream.  This implies rewriting the RTP headers of the
    outgoing packet stream, and rewriting of RTCP packets as specified
    in Section 7 of [RFC3550].

1.2.2. Transmission Modes and Packetization Modes

 This memo allows the packetization of SVC data for both single-
 session transmission (SST) and multi-session transmission (MST).  In
 the case of SST all SVC data are carried in a single RTP session.  In
 the case of MST two or more RTP sessions are used to carry the SVC
 data, in accordance with the MST-specific packetization modes defined
 in this memo, which are based on the packetization modes defined in
 [RFC6184].  In MST, each RTP session is associated with one RTP
 stream, which may carry one or more layers.
 The base layer is, by design, compatible to H.264/AVC.  During
 transmission, the associated prefix NAL units, which are introduced
 by SVC and, when present, are ignored by H.264/AVC decoders, may be
 encapsulated within the same RTP packet stream as the H.264/AVC VCL
 NAL units or in a different RTP packet stream (when MST is used).
 For convenience, the term "AVC base layer" is used to refer to the
 base layer without prefix NAL units, while the term "SVC base layer"
 is used to refer to the base layer with prefix NAL units.
 Furthermore, the base layer may have multiple temporal components
 (i.e., supporting different frame rates).  As a result, the lowest
 temporal component ("T0") of the AVC or SVC base layer is used as the
 starting point of the SVC bitstream hierarchy.
 This memo allows encapsulating in a given RTP stream any of the
 following three alternatives of layer combinations:

Wenger, et al. Standards Track [Page 13] RFC 6190 RTP Payload Format for SVC May 2011

 1. the T0 AVC base layer or the T0 SVC base layer only;
 2. one or more enhancement layers only; or
 3. the T0 SVC base layer, and one or more enhancement layers.
 SST should be used in point-to-point unicast applications and, in
 general, whenever the potential benefit of using multiple RTP
 sessions does not justify the added complexity.  When SST is used,
 the layer combination cases 1 and 3 above can be used.  When an
 H.264/AVC compatible subset of the SVC base layer is transmitted
 using SST, the packetization of [RFC6184] must be used, thus ensuring
 compatibility with [RFC6184] receivers.  When, however, one or more
 SVC quality or spatial enhancement layers are transmitted using SST,
 the packetization defined in this memo must be used.  In SST, any of
 the three [RFC6184] packetization modes, namely, single NAL unit
 mode, non-interleaved mode, and interleaved mode, can be used.
 MST should be used in a multicast session when different receivers
 may request different layers of the scalable bitstream.  An operation
 point for an SVC bitstream, as defined in this memo, corresponds to a
 set of layers that together conform to one of the profiles defined in
 Annex A or G of [H.264] and, when decoded, offer a representation of
 the original video at a certain fidelity.  The number of streams used
 in MST should be at least equal to the number of operation points
 that may be requested by the receivers.  Depending on the
 application, this may result in each layer being carried in its own
 RTP session, or in having multiple layers encapsulated within one RTP
 session.
    Informative note: Layered multicast is a term commonly used to
    describe the application where multicast is used to transmit
    layered or scalable data that has been encapsulated into more than
    one RTP session.  This application allows different receivers in
    the multicast session to receive different operation points of the
    scalable bitstream.  Layered multicast, among other application
    examples, is discussed in more detail in Section 11.2.
 When MST is used, any of the three layer combinations above can be
 used for each of the sessions.  When an H.264/AVC compatible subset
 of the SVC base layer is transmitted in its own session in MST, the
 packetization of [RFC6184] must be used, such that [RFC6184]
 receivers can be part of the MST and receive only this session.  For
 MST, this memo defines four different MST-specific packetization
 modes, namely, non-interleaved timestamp (NI-T) based mode, non-
 interleaved CS-DON (NI-C) based mode, non-interleaved combined
 timestamp and CS-DON mode (NI-TC), and interleaved CS-DON (I-C) based
 mode (detailed in Section 4.5.2).  The modes differ depending on
 whether the SVC data are allowed to be interleaved, i.e., to be
 transmitted in an order different than the intended decoding order,

Wenger, et al. Standards Track [Page 14] RFC 6190 RTP Payload Format for SVC May 2011

 and they also differ in the mechanisms provided in order to recover
 the correct decoding order of the NAL units across the multiple RTP
 sessions.  These four MST modes reuse the packetization modes
 introduced in [RFC6184] for the packetization of NAL units in each of
 their individual RTP sessions.
 As the names of the MST packetization modes imply, the NI-T, NI-C,
 and NI-TC modes do not allow interleaved transmission, while the I-C
 mode allows interleaved transmission.  With any of the three non-
 interleaved MST packetization modes, legacy [RFC6184] receivers with
 implementation of the non-interleaved mode specified in [RFC6184] can
 join a multi-session transmission of SVC, to receive the base RTP
 session encapsulated according to [RFC6184].

1.2.3. New Payload Structures

 [RFC6184] specifies three basic payload structures, namely, single
 NAL unit packet, aggregation packet, and fragmentation unit.
 Depending on the basic payload structure, an RTP packet may contain a
 NAL unit not aggregating other NAL units, one or more NAL units
 aggregated in another NAL unit, or a fragment of a NAL unit not
 aggregating other NAL units.  Each NAL unit of a type specified in
 [H.264] (i.e., 1 to 23, inclusive) may be carried in its entirety in
 a single NAL unit packet, may be aggregated in an aggregation packet,
 or may be fragmented and carried in a number of fragmentation unit
 packets.  To enable aggregation or fragmentation of NAL units while
 still ensuring that the RTP packet payload is only composed of NAL
 units, [RFC6184] introduced six new NAL unit types (24-29) to be used
 as payload structures, selected from the NAL unit types left
 unspecified in [H.264].
 This memo reuses all the payload structures used in [RFC6184].
 Furthermore, three new types of NAL units are defined: payload
 content scalability information (PACSI) NAL unit, empty NAL unit, and
 non-interleaved multi-time aggregation packet (NI-MTAP) (specified in
 Sections 4.9, 4.10, and 4.7.1, respectively).
 PACSI NAL units may be used for the following purposes:
 o  To enable MANEs to decide whether to forward, process, or discard
    aggregation packets, by checking in PACSI NAL units the
    scalability information and other characteristics of the
    aggregated NAL units, rather than looking into the aggregated NAL
    units themselves, which are defined by the video coding
    specification.

Wenger, et al. Standards Track [Page 15] RFC 6190 RTP Payload Format for SVC May 2011

 o  To enable correct decoding order recovery in MST using the NI-C or
    NI-TC mode, with the help of the CS-DON information included in
    PACSI NAL units.
 o  To improve resilience to packet losses, e.g., by utilizing the
    following data or information included in PACSI NAL units:
    repeated Supplemental Enhancement Information (SEI) messages,
    information regarding the start and end of layer representations,
    and the indices to layer representations of the lowest temporal
    subset.
 Empty NAL units may be used to enable correct decoding order recovery
 in MST using the NI-T or NI-TC mode.  NI-MTAP NAL units may be used
 to aggregate NAL units from multiple access units but without
 interleaving.

2. Conventions

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in BCP 14, RFC 2119
 [RFC2119].
 This specification uses the notion of setting and clearing a bit when
 bit fields are handled.  Setting a bit is the same as assigning that
 bit the value of 1 (On).  Clearing a bit is the same as assigning
 that bit the value of 0 (Off).

3. Definitions and Abbreviations

3.1. Definitions

 This document uses the terms and definitions of [H.264].  Section
 3.1.1 lists relevant definitions copied from [H.264] for convenience.
 When there is discrepancy, the definitions in [H.264] take
 precedence.  Section 3.1.2 gives definitions specific to this memo.
 Some of the definitions in Section 3.1.2 are also present in
 [RFC6184] and copied here with slight adaptations as needed.

3.1.1. Definitions from the SVC Specification

 access unit: A set of NAL units always containing exactly one primary
 coded picture.  In addition to the primary coded picture, an access
 unit may also contain one or more redundant coded pictures, one
 auxiliary coded picture, or other NAL units not containing slices or
 slice data partitions of a coded picture.  The decoding of an access
 unit always results in a decoded picture.

Wenger, et al. Standards Track [Page 16] RFC 6190 RTP Payload Format for SVC May 2011

 base layer: A bitstream subset that contains all the NAL units with
 the nal_unit_type syntax element equal to 1 or 5 of the bitstream and
 does not contain any NAL unit with the nal_unit_type syntax element
 equal to 14, 15, or 20 and conforms to one or more of the profiles
 specified in Annex A of [H.264].
 base quality layer representation: The layer representation of the
 target dependency representation of an access unit that is associated
 with the quality_id syntax element equal to 0.
 coded video sequence: A sequence of access units that consists, in
 decoding order, of an IDR access unit followed by zero or more non-
 IDR access units including all subsequent access units up to but not
 including any subsequent IDR access unit.
 dependency representation: A subset of Video Coding Layer (VCL) NAL
 units within an access unit that are associated with the same value
 of the dependency_id syntax element, which is provided as part of the
 NAL unit header or by an associated prefix NAL unit.  A dependency
 representation consists of one or more layer representations.
 IDR access unit: An access unit in which the primary coded picture is
 an IDR picture.
 IDR picture: Instantaneous decoding refresh picture.  A coded picture
 in which all slices of the target dependency representation within
 the access unit are I or EI slices that causes the decoding process
 to mark all reference pictures as "unused for reference" immediately
 after decoding the IDR picture.  After the decoding of an IDR picture
 all following coded pictures in decoding order can be decoded without
 inter prediction from any picture decoded prior to the IDR picture.
 The first picture of each coded video sequence is an IDR picture.
 layer representation: A subset of VCL NAL units within an access unit
 that are associated with the same values of the dependency_id and
 quality_id syntax elements, which are provided as part of the VCL NAL
 unit header or by an associated prefix NAL unit.  One or more layer
 representations represent a dependency representation.
 prefix NAL unit: A NAL unit with nal_unit_type equal to 14 that
 immediately precedes in decoding order a NAL unit with nal_unit_type
 equal to 1, 5, or 12.  The NAL unit that immediately succeeds in
 decoding order the prefix NAL unit is referred to as the associated
 NAL unit.  The prefix NAL unit contains data associated with the
 associated NAL unit, which are considered to be part of the
 associated NAL unit.

Wenger, et al. Standards Track [Page 17] RFC 6190 RTP Payload Format for SVC May 2011

 reference base picture: A reference picture that is obtained by
 decoding a base quality layer representation with the nal_ref_idc
 syntax element not equal to 0 and the store_ref_base_pic_flag syntax
 element equal to 1 of an access unit and all layer representations of
 the access unit that are referred to by inter-layer prediction of the
 base quality layer representation.  A reference base picture is not
 an output of the decoding process, but the samples of a reference
 base picture may be used for inter prediction in the decoding process
 of subsequent pictures in decoding order.  Reference base picture is
 a collective term for a reference base field or a reference base
 frame.
 scalable bitstream: A bitstream with the property that one or more
 bitstream subsets that are not identical to the scalable bitstream
 form another bitstream that conforms to the SVC specification
 [H.264].
 target dependency representation: The dependency representation of an
 access unit that is associated with the largest value of the
 dependency_id syntax element for all dependency representations of
 the access unit.
 target layer representation: The layer representation of the target
 dependency representation of an access unit that is associated with
 the largest value of the quality_id syntax element for all layer
 representations of the target dependency representation of the access
 unit.

3.1.2. Definitions Specific to This Memo

 anchor layer representation: An anchor layer representation is such a
 layer representation that, if decoding of the operation point
 corresponding to the layer starts from the access unit containing
 this layer representation, all the following layer representations of
 the layer, in output order, can be correctly decoded.  The output
 order is defined in [H.264] as the order in which decoded pictures
 are output from the decoded picture buffer of the decoder.  As H.264
 does not specify the picture display process, this more general term
 is used instead of display order.  An anchor layer representation is
 a random access point to the layer the anchor layer representation
 belongs.  However, some layer representations, succeeding an anchor
 layer representation in decoding order but preceding the anchor layer
 representation in output order, may refer to earlier layer
 representations for inter prediction, and hence the decoding may be
 incorrect if random access is performed at the anchor layer
 representation.

Wenger, et al. Standards Track [Page 18] RFC 6190 RTP Payload Format for SVC May 2011

 AVC base layer: The subset of the SVC base layer in which all prefix
 NAL units (type 14) are removed.  Note that this is equivalent to the
 term "base layer" as defined in Annex G of [H.264].
 base RTP session: When multi-session transmission is used, the RTP
 session that carries the RTP stream containing the T0 AVC base layer
 or the T0 SVC base layer, and zero or more enhancement layers.  This
 RTP session does not depend on any other RTP session as indicated by
 mechanisms defined in Section 7.2.3.  The base RTP session may carry
 NAL units of NAL unit type equal to 14 and 15.
 decoding order number (DON): A field in the payload structure or a
 derived variable indicating NAL unit decoding order.  Values of DON
 are in the range of 0 to 65535, inclusive.  After reaching the
 maximum value, the value of DON wraps around to 0.  Note that this
 definition also exists in [RFC6184] in exactly the same form.
 Empty NAL unit: A NAL unit with NAL unit type equal to 31 and sub-
 type equal to 1.  An empty NAL unit consists of only the two-byte NAL
 unit header with an empty payload.
 enhancement RTP session: When multi-session transmission is used, an
 RTP session that is not the base RTP session.  An enhancement RTP
 session typically contains an RTP stream that depends on at least one
 other RTP session as indicated by mechanisms defined in Section
 7.2.3.  A lower RTP session to an enhancement RTP session is an RTP
 session on which the enhancement RTP session depends.  The lowest RTP
 session for a receiver is the RTP session that does not depend on any
 other RTP session received by the receiver.  The highest RTP session
 for a receiver is the RTP session on which no other RTP session
 received by the receiver depends.
 cross-session decoding order number (CS-DON): A derived variable
 indicating NAL unit decoding order number over all NAL units within
 all the session-multiplexed RTP sessions that carry the same SVC
 bitstream.
 default level: The level indicated by the profile-level-id parameter.
 In Session Description Protocol (SDP) Offer/Answer, the level is
 downgradable, i.e., the answer may either use the default level or a
 lower level.  Note that this definition also exists in [RFC6184] in a
 slightly different form.
 default sub-profile: The subset of coding tools, which may be all
 coding tools of one profile or the common subset of coding tools of
 more than one profile, indicated by the profile-level-id parameter.
 In SDP Offer/Answer, the default sub-profile must be used in a

Wenger, et al. Standards Track [Page 19] RFC 6190 RTP Payload Format for SVC May 2011

 symmetric manner, i.e., the answer must either use the same sub-
 profile as the offer or reject the offer.  Note that this definition
 also exists in [RFC6184] in a slightly different form.
 enhancement layer: A layer in which at least one of the values of
 dependency_id or quality_id is higher than 0, or a layer in which
 none of the NAL units is associated with the value of temporal_id
 equal to 0.  An operation point constructed using the maximum
 temporal_id, dependency_id, and quality_id values associated with an
 enhancement layer may or may not conform to one or more of the
 profiles specified in Annex A of [H.264].
 H.264/AVC compatible: The property of a bitstream subset of
 conforming to one or more of the profiles specified in Annex A of
 [H.264].
 intra layer representation:  A layer representation that contains
 only slices that use intra prediction, and hence do not refer to any
 earlier layer representation in decoding order in the same layer.
 Note that in SVC intra prediction includes intra-layer intra
 prediction as well as inter-layer intra prediction.
 layer: A bitstream subset in which all NAL units of type 1, 5, 12,
 14, or 20 have the same values of dependency_id and quality_id,
 either directly through their NAL unit header (for NAL units of type
 14 or 20) or through association to a prefix (type 14) NAL unit (for
 NAL unit type 1, 5, or 12).  A layer may contain NAL units associated
 with more than one values of temporal_id.
 media-aware network element (MANE): A network element, such as a
 middlebox or application layer gateway that is capable of parsing
 certain aspects of the RTP payload headers or the RTP payload and
 reacting to their contents.  Note that this definition also exists in
 [RFC6184] in exactly the same form.
    Informative note: The concept of a MANE goes beyond normal routers
    or gateways in that a MANE has to be aware of the signaling (e.g.,
    to learn about the payload type mappings of the media streams),
    and in that it has to be trusted when working with Secure Real-
    time Transport Protocol (SRTP).  The advantage of using MANEs is
    that they allow packets to be dropped according to the needs of
    the media coding.  For example, if a MANE has to drop packets due
    to congestion on a certain link, it can identify and remove those
    packets whose elimination produces the least adverse effect on the
    user experience.  After dropping packets, MANEs must rewrite RTCP
    packets to match the changes to the RTP packet stream as specified
    in Section 7 of [RFC3550].

Wenger, et al. Standards Track [Page 20] RFC 6190 RTP Payload Format for SVC May 2011

 multi-session transmission: The transmission mode in which the SVC
 stream is transmitted over multiple RTP sessions.  Dependency between
 RTP sessions MUST be signaled according to Section 7.2.3 of this
 memo.
 NAL unit decoding order: A NAL unit order that conforms to the
 constraints on NAL unit order given in Section G.7.4.1.2 in [H.264].
 Note that this definition also exists in [RFC6184] in a slightly
 different form.
 NALU-time: The value that the RTP timestamp would have if the NAL
 unit would be transported in its own RTP packet.  Note that this
 definition also exists in [RFC6184] in exactly the same form.
 operation point: An operation point is identified by a set of values
 of temporal_id, dependency_id, and quality_id.  A bitstream
 corresponding to an operation point can be constructed by removing
 all NAL units associated with a higher value of dependency_id, and
 all NAL units associated with the same value of dependency_id but
 higher values of quality_id or temporal_id.  An operation point
 bitstream conforms to at least one of the profiles defined in Annex A
 or G of [H.264], and offers a representation of the original video
 signal at a certain fidelity.
    Informative note: Additional NAL units may be removed (with lower
    dependency_id or same dependency_id but lower quality_id) if they
    are not required for decoding the bitstream at the particular
    operation point.  The resulting bitstream, however, may no longer
    conform to any of the profiles defined in Annex A or G of [H.264].
 operation point representation: The set of all NAL units of an
 operation point within the same access unit.
 RTP packet stream: A sequence of RTP packets with increasing sequence
 numbers (except for wrap-around), identical payload type and
 identical SSRC (Synchronization Source), carried in one RTP session.
 Within the scope of this memo, one RTP packet stream is utilized to
 transport one or more layers.
 single-session transmission: The transmission mode in which the SVC
 bitstream is transmitted over a single RTP session.
 SVC base layer: The layer that includes all NAL units associated with
 dependency_id and quality_id values both equal to 0, including prefix
 NAL units (NAL unit type 14).

Wenger, et al. Standards Track [Page 21] RFC 6190 RTP Payload Format for SVC May 2011

 SVC enhancement layer: A layer in which at least one of the values of
 dependency_id or quality_id is higher than 0.  An operation point
 constructed using the maximum dependency_id and quality_id values and
 any temporal_id value associated with an SVC enhancement layer does
 not conform to any of the profiles specified in Annex A of [H.264].
 SVC NAL unit: A NAL unit of NAL unit type 14, 15, or 20 as specified
 in Annex G of [H.264].
 SVC NAL unit header: A four-byte header resulting from the addition
 of a three-byte SVC-specific header extension added in NAL unit types
 14 and 20.
 SVC RTP session: Either the base RTP session or an enhancement RTP
 session.
 T0 AVC base layer: A subset of the AVC base layer constructed by
 removing all VCL NAL units associated with temporal_id values higher
 than 0 and non-VCL NAL units and SEI messages associated only with
 the VCL NAL units being removed.
 T0 SVC base layer: A subset of the SVC base layer constructed by
 removing all VCL NAL units associated with temporal_id values higher
 than 0 as well as prefix NAL units, non-VCL NAL units, and SEI
 messages associated only with the VCL NAL units being removed.
 transmission order: The order of packets in ascending RTP sequence
 number order (in modulo arithmetic).  Within an aggregation packet,
 the NAL unit transmission order is the same as the order of
 appearance of NAL units in the packet.  Note that this definition
 also exists in [RFC6184] in exactly the same form.

3.2. Abbreviations

 In addition to the abbreviations defined in [RFC6184], the following
 abbreviations are used in this memo.
    CGS:        Coarse-Grain Scalability
    CS-DON:     Cross-Session Decoding Order Number
    MGS:        Medium-Grain Scalability
    MST:        Multi-Session Transmission
    PACSI:      Payload Content Scalability Information
    SST:        Single-Session Transmission
    SNR:        Signal-to-Noise Ratio
    SVC:        Scalable Video Coding

Wenger, et al. Standards Track [Page 22] RFC 6190 RTP Payload Format for SVC May 2011

4. RTP Payload Format

4.1. RTP Header Usage

 In addition to Section 5.1 of [RFC6184], the following rules apply.
 o Setting of the M bit:
 The M bit of an RTP packet for which the packet payload is an NI-MTAP
 MUST be equal to 1 if the last NAL unit, in decoding order, of the
 access unit associated with the RTP timestamp is contained in the
 packet.
 o Setting of the RTP timestamp:
 For an RTP packet for which the packet payload is an empty NAL unit,
 the RTP timestamp must be set according to Section 4.10.
 For an RTP packet for which the packet payload is a PACSI NAL unit,
 the RTP timestamp MUST be equal to the NALU-time of the next non-
 PACSI NAL unit in transmission order.  Recall that the NALU-time of a
 NAL unit in an MTAP is defined in [RFC6184] as the value that the RTP
 timestamp would have if that NAL unit would be transported in its own
 RTP packet.
 o Setting of the SSRC:
 For both SST and MST, the SSRC values MUST be set according to
 [RFC3550].

4.2. NAL Unit Extension and Header Usage

4.2.1. NAL Unit Extension

 This memo specifies a NAL unit extension mechanism to allow for
 introduction of new types of NAL units, beyond the three NAL unit
 types left undefined in [RFC6184] (i.e., 0, 30, and 31).  The
 extension mechanism utilizes the NAL unit type value 31 and is
 specified as follows.  When the NAL unit type value is equal to 31,
 the one-byte NAL unit header consisting of the F, NRI, and Type
 fields as specified in Section 1.1.3 is extended by one additional
 octet, which consists of a 5-bit field named Subtype and three 1-bit
 fields named J, K, and L, respectively.  The additional octet is
 shown in the following figure.

Wenger, et al. Standards Track [Page 23] RFC 6190 RTP Payload Format for SVC May 2011

       +---------------+
       |0|1|2|3|4|5|6|7|
       +-+-+-+-+-+-+-+-+
       | Subtype |J|K|L|
       +---------------+
 The Subtype value determines the (extended) NAL unit type of this NAL
 unit.  The interpretation of the fields J, K, and L depends on the
 Subtype.  The semantics of the fields are as follows.
 When Subtype is equal to 1, the NAL unit is an empty NAL unit as
 specified in Section 4.10.  When Subtype is equal to 2, the NAL unit
 is an NI-MTAP NAL unit as specified in Section 4.7.1.  All other
 values of Subtype (0, 3-31) are reserved for future extensions, and
 receivers MUST ignore the entire NAL unit when Subtype is equal to
 any of these reserved values.

4.2.2. NAL Unit Header Usage

 The structure and semantics of the NAL unit header according to the
 H.264 specification [H.264] were introduced in Section 1.1.3.  This
 section specifies the extended semantics of the NAL unit header
 fields F, NRI, I, PRID, DID, QID, TID, U, and D, according to this
 memo.  When the Type field is equal to 31, the semantics of the
 fields in the extension NAL unit header were specified in Section
 4.2.1.
 The semantics of F specified in Section 5.3 of [RFC6184] also apply
 in this memo.  That is, a value of 0 for F indicates that the NAL
 unit type octet and payload should not contain bit errors or other
 syntax violations, whereas a value of 1 for F indicates that the NAL
 unit type octet and payload may contain bit errors or other syntax
 violations.  MANEs SHOULD set the F bit to indicate bit errors in the
 NAL unit.
 For NRI, for a bitstream conforming to one of the profiles defined in
 Annex A of [H.264] and transported using [RFC6184], the semantics
 specified in Section 5.3 of [RFC6184] apply, i.e., NRI also indicates
 the relative importance of NAL units.  For a bitstream conforming to
 one of the profiles defined in Annex G of [H.264] and transported
 using this memo, in addition to the semantics specified in Annex G of
 [H.264], NRI also indicates the relative importance of NAL units
 within a layer.
 For I, in addition to the semantics specified in Annex G of [H.264],
 according to this memo, MANEs MAY use this information to protect NAL
 units with I equal to 1 better than NAL units with I equal to 0.
 MANEs MAY also utilize information of NAL units with I equal to 1 to

Wenger, et al. Standards Track [Page 24] RFC 6190 RTP Payload Format for SVC May 2011

 decide when to forward more packets for an RTP packet stream.  For
 example, when it is detected that spatial layer switching has
 happened such that the operation point has changed to a higher value
 of DID, MANEs MAY start to forward NAL units with the higher value of
 DID only after forwarding a NAL unit with I equal to 1 with the
 higher value of DID.
 Note that, in the context of this section, "protecting a NAL unit"
 means any RTP or network transport mechanism that could improve the
 probability of successful delivery of the packet conveying the NAL
 unit, including applying a Quality of Service (QoS) enabled network,
 Forward Error Correction (FEC), retransmissions, and advanced
 scheduling behavior, whenever possible.
 For PRID, the semantics specified in Annex G of [H.264] apply.  Note
 that MANEs implementing unequal error protection MAY use this
 information to protect NAL units with smaller PRID values better than
 those with larger PRID values, for example, by including only the
 more important NAL units in a FEC protection mechanism.  The
 importance for the decoding process decreases as the PRID value
 increases.
 For DID, QID, or TID, in addition to the semantics specified in Annex
 G of [H.264], according to this memo, values of DID, QID, or TID
 indicate the relative importance in their respective dimension.  A
 lower value of DID, QID, or TID indicates a higher importance if the
 other two components are identical.  MANEs MAY use this information
 to protect more important NAL units better than less important NAL
 units.
 For U, in addition to the semantics specified in Annex G of [H.264],
 according to this memo, MANEs MAY use this information to protect NAL
 units with U equal to 1 better than NAL units with U equal to 0.
 For D, in addition to the semantics specified in Annex G of [H.264],
 according to this memo, MANEs MAY use this information to determine
 whether a given NAL unit is required for successfully decoding a
 certain Operation Point of the SVC bitstream, hence to decide whether
 to forward the NAL unit.

4.3. Payload Structures

 The NAL unit structure is central to H.264/AVC, [RFC6184], as well as
 SVC and this memo.  In H.264/AVC and SVC, all coded bits for
 representing a video signal are encapsulated in NAL units.  In
 [RFC6184], each RTP packet payload is structured as a NAL unit, which
 contains one or a part of one NAL unit specified in H.264/AVC, or
 aggregates one or more NAL units specified in H.264/AVC.

Wenger, et al. Standards Track [Page 25] RFC 6190 RTP Payload Format for SVC May 2011

 [RFC6184] specifies three basic payload structures (in Section 5.2 of
 [RFC6184]): single NAL unit packet, aggregation packet, fragmentation
 unit, and six new types (24 to 29) of NAL units.  The value of the
 Type field of the RTP packet payload header (i.e., the first byte of
 the payload) may be equal to any value from 1 to 23 for a single NAL
 unit packet, any value from 24 to 27 for an aggregation packet, and
 28 or 29 for a fragmentation unit.
 In addition to the NAL unit types defined originally for H.264/AVC,
 SVC defines three new NAL unit types specifically for SVC: coded
 slice in scalable extension NAL units (type 20), prefix NAL units
 (type 14), and subset sequence parameter set NAL units (type 15), as
 described in Section 1.1.
 This memo further introduces three new types of NAL units, PACSI NAL
 unit (NAL unit type 30) as specified in Section 4.9, empty NAL unit
 (type 31, subtype 1) as specified in Section 4.10, and NI-MTAP NAL
 unit (type 31, subtype 2) as specified in Section 4.7.1.
 The RTP packet payload structure in [RFC6184] is maintained with
 slight extensions in this memo, as follows.  Each RTP packet payload
 is still structured as a NAL unit, which contains one or a part of
 one NAL unit specified in H.264/AVC and SVC, or contains one PACSI
 NAL unit or one empty NAL unit, or aggregates zero or more NAL units
 specified in H.264/AVC and SVC, zero or one PACSI NAL unit, and zero
 or more empty NAL units.
 In this memo, one of the three basic payload structures,
 fragmentation unit, remains the same as in [RFC6184], and the other
 two, single NAL unit packet and aggregation packet, are extended as
 follows.  The value of the Type field of the payload header may be
 equal to any value from 1 to 23, inclusive, and 30 to 31, inclusive,
 for a single NAL unit packet, and any value from 24 to 27, inclusive,
 and 31, for an aggregation packet.  When the Type field of the
 payload header is equal to 31 and the Subtype field of the payload
 header is equal to 2, the packet is an aggregation packet (containing
 an NI-MTAP NAL unit).  When the Type field of the payload header is
 equal to 31 and the Subtype field of the payload header is equal to
 1, the packet is a single NAL unit packet (containing an empty NAL
 unit).
 Note that, in this memo, the length of the payload header varies
 depending on the value of the Type field in the first byte of the RTP
 packet payload.  If the value is equal to 14, 20, or 30, the first
 four bytes of the packet payload form the payload header; otherwise,
 if the value is equal to 31, the first two bytes of the payload form
 the payload header; otherwise, the payload header is the first byte
 of the packet payload.

Wenger, et al. Standards Track [Page 26] RFC 6190 RTP Payload Format for SVC May 2011

 Table 1 lists the NAL unit types introduced in SVC and this memo and
 where they are described in this memo.  Table 2 summarizes the basic
 payload structure types for all NAL unit types when they are directly
 used as RTP packet payloads according to this memo.  Table 3
 summarizes the NAL unit types allowed to be aggregated (i.e., used as
 aggregation units in aggregation packets) or fragmented (i.e.,
 carried in fragmentation units) according to this memo.
 Table 1.  NAL unit types introduced in SVC and this memo
 Type  Subtype  NAL Unit Name                Section Numbers
 -----------------------------------------------------------
 14     -       Prefix NAL unit                    1.1
 15     -       Subset sequence parameter set      1.1
 20     -       Coded slice in scalable extension  1.1
 30     -       PACSI NAL unit                     4.9
 31     0       reserved                           4.2.1
 31     1       Empty NAL unit                     4.10
 31     2       NI-MTAP                            4.7.1
 31     3-31    reserved                           4.2.1
 Table 2.  Basic payload structure types for all NAL unit
 types when they are directly used as RTP packet payloads
 Type   Subtype    Basic Payload Structure
 ------------------------------------------
 0      -          reserved
 1-23   -          Single NAL Unit Packet
 24-27  -          Aggregation Packet
 28-29  -          Fragmentation Unit
 30     -          Single NAL Unit Packet
 31     0          reserved
 31     1          Single NAL Unit Packet
 31     2          Aggregation Packet
 31     3-31       reserved

Wenger, et al. Standards Track [Page 27] RFC 6190 RTP Payload Format for SVC May 2011

 Table 3.  Summary of the NAL unit types allowed to be
 aggregated or fragmented (yes = allowed, no = disallowed,
 - = not applicable/not specified)
 Type  Subtype STAP-A STAP-B MTAP16 MTAP24 FU-A FU-B NI-MTAP
 -------------------------------------------------------------
 0     -          -      -      -      -     -     -     -
 1-23  -        yes    yes    yes    yes   yes   yes   yes
 24-29 -         no     no     no     no    no    no    no
 30    -        yes    yes    yes    yes    no    no   yes
 31    0          -      -      -      -     -     -     -
 31    1        yes     no     no     no    no    no   yes
 31    2         no     no     no     no    no    no    no
 31    3-31       -      -      -      -     -     -     -

4.4. Transmission Modes

 This memo enables transmission of an SVC bitstream over one or more
 RTP sessions.  If only one RTP session is used for transmission of
 the SVC bitstream, the transmission mode is referred to as single-
 session transmission (SST); otherwise (more than one RTP session is
 used for transmission of the SVC bitstream), the transmission mode is
 referred to as multi-session transmission (MST).
 SST SHOULD be used for point-to-point unicast scenarios, while MST
 SHOULD be used for point-to-multipoint multicast scenarios where
 different receivers requires different operation points of the same
 SVC bitstream, to improve bandwidth utilizing efficiency.
 If the OPTIONAL mst-mode media type parameter (see Section 7.1) is
 not present, SST MUST be used; otherwise (mst-mode is present), MST
 MUST be used.

4.5. Packetization Modes

4.5.1. Packetization Modes for Single-Session Transmission

 When SST is in use, Section 5.4 of [RFC6184] applies with the
 following extensions.
 The packetization modes specified in Section 5.4 of [RFC6184],
 namely, single NAL unit mode, non-interleaved mode, and interleaved
 mode, are also referred to as session packetization modes.  Table 4
 summarizes the allowed session packetization modes for SST.

Wenger, et al. Standards Track [Page 28] RFC 6190 RTP Payload Format for SVC May 2011

 Table 4.  Summary of allowed session packetization modes
 (denoted as "Session Mode" for simplicity) for SST (yes =
 allowed, no = disallowed)
 Session Mode               Allowed
 -------------------------------------
 Single NAL Unit Mode         yes
 Non-Interleaved Mode         yes
 Interleaved Mode             yes
 For NAL unit types in the range of 0 to 29, inclusive, the NAL unit
 types allowed to be directly used as packet payloads for each session
 packetization mode are the same as specified in Section 5.4 of
 [RFC6184].  For other NAL unit types, which are newly introduced in
 this memo, the NAL unit types allowed to be directly used as packet
 payloads for each session packetization mode are summarized in Table
 5.
 Table 5.  New NAL unit types allowed to be directly used
 as packet payloads for each session packetization mode
 (yes = allowed, no = disallowed, - = not applicable/not specified)
 Type   Subtype    Single NAL    Non-Interleaved    Interleaved
                   Unit Mode           Mode             Mode
 -------------------------------------------------------------
 30     -            yes               no               no
 31     0              -                -                -
 31     1            yes              yes               no
 31     2             no              yes               no
 31     3-31           -                -                -

4.5.2. Packetization Modes for Multi-Session Transmission

 For MST, this memo specifies four MST packetization modes:
 o  Non-interleaved timestamp based mode (NI-T);
 o  Non-interleaved cross-session decoding order number (CS-DON) based
    mode (NI-C);
 o  Non-interleaved combined timestamp and CS-DON mode (NI-TC); and
 o  Interleaved CS-DON (I-C) mode.
 These four modes differ in two ways.  First, they differ in terms of
 whether NAL units are required to be transmitted within each RTP
 session in decoding order (i.e., non-interleaved), or they are
 allowed to be transmitted in a different order (i.e., interleaved).

Wenger, et al. Standards Track [Page 29] RFC 6190 RTP Payload Format for SVC May 2011

 Second, they differ in the mechanisms they provide in order to
 recover the correct decoding order of the NAL units across all RTP
 sessions involved.
 The NI-T, NI-C, and NI-TC modes do not allow interleaving, and are
 thus targeted for systems that require relatively low end-to-end
 latency, e.g., conversational systems.  The I-C mode allows
 interleaving and is thus targeted for systems that do not require
 very low end-to-end latency.  The benefits of interleaving are the
 same as that of the interleaved mode specified in [RFC6184].
 The NI-T mode uses timestamps to recover the decoding order of NAL
 units, whereas the NI-C and I-C modes both use the CS-DON mechanism
 (explained later) to do so.  The NI-TC mode provides both timestamps
 and the CS-DON method; receivers in this case may choose to use
 either method for performing decoding order recovery.  The MST
 packetization mode in use MUST be signaled by the value of the
 OPTIONAL mst-mode media type parameter.  The used MST packetization
 mode governs which session packetization modes are allowed in the
 associated RTP sessions, which in turn govern which NAL unit types
 are allowed to be directly used as RTP packet payloads.
 Table 6 summarizes the allowed session packetization modes for NI-T,
 NI-C, and NI-TC.  Table 7 summarizes the allowed session
 packetization modes for I-C.
 Table 6.  Summary of allowed session packetization modes
 (denoted as "Session Mode" for simplicity) for NI-T, NI-C, and
 NI-TC (yes = allowed, no = disallowed)
 Session Mode            Base Session    Enhancement Session
 -----------------------------------------------------------
 Single NAL Unit Mode         yes             no
 Non-Interleaved Mode         yes            yes
 Interleaved Mode              no             no
 Table 7.  Summary of allowed session packetization modes
 (denoted as "Session Mode" for simplicity) for I-C
 (yes = allowed, no = disallowed)
 Session Mode            Base Session    Enhancement Session
 -----------------------------------------------------------
 Single NAL Unit Mode          no             no
 Non-Interleaved Mode          no             no
 Interleaved Mode             yes            yes

Wenger, et al. Standards Track [Page 30] RFC 6190 RTP Payload Format for SVC May 2011

 For NAL unit types in the range of 0 to 29, inclusive, the NAL unit
 types allowed to be directly used as packet payloads for each session
 packetization mode are the same as specified in Section 5.4 of
 [RFC6184].  For other NAL unit types, which are newly introduced in
 this memo, the NAL unit types allowed to be directly used as packet
 payloads for each allowed session packetization mode for NI-T, NI-C,
 NI-TC, and I-C are summarized in Tables 8, 9, 10, and 11,
 respectively.
 Table 8.  New NAL unit types allowed to be directly used
 as packet payloads for each allowed session packetization
 mode when NI-T is in use (yes = allowed, no = disallowed,
 - = not applicable/not specified)
 Type   Subtype    Single NAL    Non-Interleaved
                   Unit Mode           Mode
 ---------------------------------------------------
 30     -            yes               no
 31     0              -                -
 31     1            yes              yes
 31     2             no              yes
 31     3-31           -                -
 Table 9.  New NAL unit types allowed to be directly used
 as packet payloads for each allowed session packetization
 mode when NI-C is in use (yes = allowed, no = disallowed,
 - = not applicable/not specified)
 Type   Subtype    Single NAL    Non-Interleaved
                   Unit Mode           Mode
 ---------------------------------------------------
 30     -            yes              yes
 31     0              -                -
 31     1             no               no
 31     2             no              yes
 31     3-31           -                -

Wenger, et al. Standards Track [Page 31] RFC 6190 RTP Payload Format for SVC May 2011

 Table 10.  New NAL unit types allowed to be directly used
 as packet payloads for each allowed session packetization
 mode when NI-TC is in use (yes = allowed, no = disallowed,
 - = not applicable/not specified)
 Type   Subtype    Single NAL    Non-Interleaved
                   Unit Mode           Mode
 ---------------------------------------------------
 30     -            yes              yes
 31     0              -                -
 31     1             yes             yes
 31     2             no              yes
 31     3-31           -                -
 Table 11.  New NAL unit types allowed to be directly used
 as packet payloads for the allowed session packetization
 mode when I-C is in use (yes = allowed, no = disallowed,
 - = not applicable/not specified)
 Type   Subtype    Interleaved Mode
 ------------------------------------
 30     -               no
 31     0                -
 31     1               no
 31     2               no
 31     3-31             -
 When MST is in use and the MST packetization mode in use is NI-C,
 empty NAL units (type 31, subtype 1) MUST NOT be used, i.e., no RTP
 packet is allowed to contain one or more empty NAL units.
 When MST is in use and the MST packetization mode in use is I-C, both
 empty NAL units (type 31, subtype 1) and NI-MTAP NAL units (type 31,
 subtype 2) MUST NOT be used, i.e., no RTP packet is allowed to
 contain one or more empty NAL units or an NI-MTAP NAL unit.

4.6. Single NAL Unit Packets

 Section 5.6 of [RFC6184] applies with the following extensions.
 The payload of a single NAL unit packet MAY be a PACSI NAL unit (Type
 30) or an empty NAL unit (Type 31 and Subtype 1), in addition to a
 NAL unit with NAL unit type equal to any value from 1 to 23,
 inclusive.

Wenger, et al. Standards Track [Page 32] RFC 6190 RTP Payload Format for SVC May 2011

 If the Type field of the first byte of the payload is not equal to
 31, the payload header is the first byte of the payload.  Otherwise,
 (the Type field of the first byte of the payload is equal to 31), the
 payload header is the first two bytes of the payload.

4.7. Aggregation Packets

 In addition to Section 5.7 of [RFC6184], the following applies in
 this memo.

4.7.1. Non-Interleaved Multi-Time Aggregation Packets (NI-MTAPs)

 One new NAL unit type introduced in this memo is the non-interleaved
 multi-time aggregation packet (NI-MTAP).  An NI-MTAP consists of one
 or more non-interleaved multi-time aggregation units.
 The NAL units contained in NI-MTAPs MUST be aggregated in decoding
 order.
 A non-interleaved multi-time aggregation unit for the NI-MTAP
 consists of 16 bits of unsigned size information of the following NAL
 unit (in network byte order), and 16 bits (in network byte order) of
 timestamp offset (TS offset) for the NAL unit.  The structure is
 presented in Figure 1.  The starting or ending position of an
 aggregation unit within a packet may or may not be on a 32-bit word
 boundary.  The NAL units in the NI-MTAP are ordered in NAL unit
 decoding order.
 The Type field of the NI-MTAP MUST be set equal to "31".
 The F bit MUST be set to 0 if all the F bits of the aggregated NAL
 units are zero; otherwise, it MUST be set to 1.
 The value of NRI MUST be the maximum value of NRI across all NAL
 units carried in the NI-MTAP packet.
 The field Subtype MUST be equal to 2.
 If the field J is equal to 1, the optional DON field MUST be present
 for each of the non-interleaved multi-time aggregation units.  For
 SST, the J field MUST be equal to 0.  For MST, in the NI-T mode the J
 field MUST be equal to 0, whereas in the NI-C or NI-TC mode the J
 field MUST be equal to 1.  When the NI-C or NI-TC mode is in use, the
 DON field, when present, MUST represent the CS-DON value for the
 particular NAL unit as defined in Section 6.2.2.
 The fields K and L MUST be both equal to 0.

Wenger, et al. Standards Track [Page 33] RFC 6190 RTP Payload Format for SVC May 2011

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 :        NAL unit size          |        TS offset              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        DON (optional)         |                               |
 |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    NAL unit                   |
 |                                                               |
 |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                               :
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure 1.  Non-interleaved multi-time aggregation unit for NI-MTAP
 Let TS be the RTP timestamp of the packet carrying the NAL unit.
 Recall that the NALU-time of a NAL unit in an MTAP is defined in
 [RFC6184] as the value that the RTP timestamp would have if that NAL
 unit would be transported in its own RTP packet.  The timestamp
 offset field MUST be set to a value equal to the value of the
 following formula:
    if NALU-time >= TS, TS offset = NALU-time - TS
    else, TS offset = NALU-time + (2^32 - TS)
 For the "earliest" multi-time aggregation unit in an NI-MTAP, the
 timestamp offset MUST be zero.  Hence, the RTP timestamp of the NI-
 MTAP itself is identical to the earliest NALU-time.
    Informative note: The "earliest" multi-time aggregation unit is
    the one that would have the smallest extended RTP timestamp among
    all the aggregation units of an NI-MTAP if the aggregation units
    were encapsulated in single NAL unit packets.  An extended
    timestamp is a timestamp that has more than 32 bits and is capable
    of counting the wraparound of the timestamp field, thus enabling
    one to determine the smallest value if the timestamp wraps.  Such
    an "earliest" aggregation unit may or may not be the first one in
    the order in which the aggregation units are encapsulated in an
    NI-MTAP.  The "earliest" NAL unit need not be the same as the
    first NAL unit in the NAL unit decoding order either.
 Figure 2 presents an example of an RTP packet that contains an NI-
 MTAP that contains two non-interleaved multi-time aggregation units,
 labeled as 1 and 2 in the figure.

Wenger, et al. Standards Track [Page 34] RFC 6190 RTP Payload Format for SVC May 2011

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          RTP Header                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |F|NRI|  Type   | Subtype |J|K|L|                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
 |                                                               |
 |        Non-interleaved multi-time aggregation unit #1         |
 :                                                               :
 |                                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                 |  Non-interleaved multi-time |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                             |
 |                      aggregation unit #2                      |
 :                                                               :
 |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                               :...OPTIONAL RTP padding        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure 2.  An RTP packet including an NI-MTAP containing two
 non-interleaved multi-time aggregation units

4.8. Fragmentation Units (FUs)

 Section 5.8 of [RFC6184] applies.
    Informative note: In case a NAL unit with the four-byte SVC NAL
    unit header is fragmented, the three-byte SVC-specific header
    extension is considered as part of the NAL unit payload.  That is,
    the three-byte SVC-specific header extension is only available in
    the first fragment of the fragmented NAL unit.

4.9. Payload Content Scalability Information (PACSI) NAL Unit

 Another new type of NAL unit specified in this memo is the payload
 content scalability information (PACSI) NAL unit.  The Type field of
 PACSI NAL units MUST be equal to 30 (a NAL unit type value left
 unspecified in [H.264] and [RFC6184]).  A PACSI NAL unit MAY be
 carried in a single NAL unit packet or an aggregation packet, and
 MUST NOT be fragmented.
 PACSI NAL units may be used for the following purposes:
 o  To enable MANEs to decide whether to forward, process, or discard
    aggregation packets, by checking in PACSI NAL units the
    scalability information and other characteristics of the

Wenger, et al. Standards Track [Page 35] RFC 6190 RTP Payload Format for SVC May 2011

    aggregated NAL units, rather than looking into the aggregated NAL
    units themselves, which are defined by the video coding
    specification;
 o  To enable correct decoding order recovery in MST using the NI-C or
    NI-TC mode, with the help of the CS-DON information included in
    PACSI NAL units; and
 o  To improve resilience to packet losses, e.g., by utilizing the
    following data or information included in PACSI NAL units:
    repeated Supplemental Enhancement Information (SEI) messages,
    information regarding the start and end of layer representations,
    and the indices to layer representations of the lowest temporal
    subset.
 PACSI NAL units MAY be ignored in the NI-T mode without affecting the
 decoding order recovery process.
 When a PACSI NAL unit is present in an aggregation packet, the
 following applies.
 o  The PACSI NAL unit MUST be the first aggregated NAL unit in the
    aggregation packet.
 o  There MUST be at least one additional aggregated NAL unit in the
    aggregation packet.
 o  The RTP header fields and the payload header fields of the
    aggregation packet are set as if the PACSI NAL unit was not
    included in the aggregation packet.
 o  If the aggregation packet is an MTAP16, MTAP24, or NI-MTAP with
    the J field equal to 1, the decoding order number (DON) for the
    PACSI NAL unit MUST be set to indicate that the PACSI NAL unit has
    an identical DON to the first NAL unit in decoding order among the
    remaining NAL units in the aggregation packet.
 When a PACSI NAL unit is included in a single NAL unit packet, it is
 associated with the next non-PACSI NAL unit in transmission order,
 and the RTP header fields of the packet are set as if the next non-
 PACSI NAL unit in transmission order was included in a single NAL
 unit packet.
 The PACSI NAL unit structure is as follows.  The first four octets
 are exactly the same as the four-byte SVC NAL unit header discussed
 in Section 1.1.3.  They are followed by one octet containing several
 flags, then five optional octets, and finally zero or more SEI NAL
 units.  Each SEI NAL unit is preceded by a 16-bit unsigned size field

Wenger, et al. Standards Track [Page 36] RFC 6190 RTP Payload Format for SVC May 2011

 (in network byte order) that indicates the size of the following NAL
 unit in bytes (excluding these two octets, but including the NAL unit
 header octet of the SEI NAL unit).  Figure 3 illustrates the PACSI
 NAL unit structure and an example of a PACSI NAL unit containing two
 SEI NAL units.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |F|NRI|  Type   |R|I|   PRID    |N| DID |  QID  | TID |U|D|O| RR|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |X|Y|T|A|P|C|S|E| TL0PICIDX (o) |        IDRPICID (o)           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          DONC (o)             |        NAL unit size 1        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                 SEI NAL unit 1                                |
 |                                                               |
 |               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               |        NAL unit size 2        |               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
 |                                                               |
 |            SEI NAL unit 2                                     |
 |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure 3.  PACSI NAL unit structure.  Fields suffixed by
 "(o)" are OPTIONAL.
 The bits A, P, and C are specified only if the bit X is equal to 1.
 The bits S and E are specified, and the fields TL0PICIDX and IDRPICID
 are present, only if the bit Y is equal to 1.  The field DONC is
 present only if the bit T is equal to 1.  The field T MUST be equal
 to 0 if the PACSI NAL unit is contained in an STAP-B, MTAP16, MTAP24,
 or NI-MTAP with the J field equal to 1.
 The values of the fields in PACSI NAL unit MUST be set as follows.
 o  The F bit MUST be set to 1 if the F bit in at least one of the
    remaining NAL units in the aggregation packet is equal to 1 (when
    the PACSI NAL unit is included in an aggregation packet) or if the
    next non-PACSI NAL unit in transmission order has the F bit equal
    to 1 (when the PACSI NAL unit is included in a single NAL unit
    packet).  Otherwise, the F bit MUST be set to 0.

Wenger, et al. Standards Track [Page 37] RFC 6190 RTP Payload Format for SVC May 2011

 o  The NRI field MUST be set to the highest value of NRI field among
    all the remaining NAL units in the aggregation packet (when the
    PACSI NAL unit is included in an aggregation packet) or the value
    of the NRI field of the next non-PACSI NAL unit in transmission
    order (when the PACSI NAL unit is included in a single NAL unit
    packet).
 o  The Type field MUST be set to 30.
 o  The R bit MUST be set to 1.  Receivers MUST ignore the value of R.
 o  The I bit MUST be set to 1 if the I bit of at least one of the
    remaining NAL units in the aggregation packet is equal to 1 (when
    the PACSI NAL unit is included in an aggregation packet) or if the
    I bit of the next non-PACSI NAL unit in transmission order is
    equal to 1 (when the PACSI NAL unit is included in a single NAL
    unit packet).  Otherwise, the I bit MUST be set to 0.
 o  The PRID field MUST be set to the lowest value of the PRID values
    of the remaining NAL units in the aggregation packet (when the
    PACSI NAL unit is included in an aggregation packet) or the PRID
    value of the next non-PACSI NAL unit in transmission order (when
    the PACSI NAL unit is included in a single NAL unit packet).
 o  The N bit MUST be set to 1 if the N bit of all the remaining NAL
    units in the aggregation packet is equal to 1 (when the PACSI NAL
    unit is included in an aggregation packet) or if the N bit of the
    next non-PACSI NAL unit in transmission order is equal to 1 (when
    the PACSI NAL unit is included in a single NAL unit packet).
    Otherwise, the N bit MUST be set to 0.
 o  The DID field MUST be set to the lowest value of the DID values of
    the remaining NAL units in the aggregation packet (when the PACSI
    NAL unit is included in an aggregation packet) or the DID value of
    the next non-PACSI NAL unit in transmission order (when the PACSI
    NAL unit is included in a single NAL unit packet).
 o  The QID field MUST be set to the lowest value of the QID values of
    the remaining NAL units with the lowest value of DID in the
    aggregation packet (when the PACSI NAL unit is included in an
    aggregation packet) or the QID value of the next non-PACSI NAL
    unit in transmission order (when the PACSI NAL unit is included in
    a single NAL unit packet).
 o  The TID field MUST be set to the lowest value of the TID values of
    the remaining NAL units with the lowest value of DID in the
    aggregation packet (when the PACSI NAL unit is included in an

Wenger, et al. Standards Track [Page 38] RFC 6190 RTP Payload Format for SVC May 2011

    aggregation packet) or the TID value of the next non-PACSI NAL
    unit in transmission order (when the PACSI NAL unit is included in
    a single NAL unit packet).
 o  The U bit MUST be set to 1 if the U bit of at least one of the
    remaining NAL units in the aggregation packet is equal to 1 (when
    the PACSI NAL unit is included in an aggregation packet) or if the
    U bit of the next non-PACSI NAL unit in transmission order is
    equal to 1 (when the PACSI NAL unit is included in a single NAL
    unit packet).  Otherwise, the U bit MUST be set to 0.
 o  The D bit MUST be set to 1 if the D value of all the remaining NAL
    units in the aggregation packet is equal to 1 (when the PACSI NAL
    unit is included in an aggregation packet) or if the D bit of the
    next non-PACSI NAL unit in transmission order is equal to 1 (when
    the PACSI NAL unit is included in a single NAL unit packet).
    Otherwise, the D bit MUST be set to 0.
 o  The O bit MUST be set to 1 if the O bit of at least one of the
    remaining NAL units in the aggregation packet is equal to 1 (when
    the PACSI NAL unit is included in an aggregation packet) or if the
    O bit of the next non-PACSI NAL unit in transmission order is
    equal to 1 (when the PACSI NAL unit is included in a single NAL
    unit packet).  Otherwise, the O bit MUST be set to 0.
 o  The RR field MUST be set to "11" (in binary form).  Receivers MUST
    ignore the value of RR.
 o  If the X bit is equal to 1, the bits A, P, and C are specified as
    below.  Otherwise, the bits A, P, and C are unspecified, and
    receivers MUST ignore the values of these bits.  The X bit SHOULD
    be identical for all the PACSI NAL units in all the RTP sessions
    carrying the same SVC bitstream.
 o  If the Y bit is equal to 1, the OPTIONAL fields TL0PICIDX and
    IDRPICID MUST be present and specified as below, and the bits S
    and E are also specified as below.  Otherwise, the fields
    TL0PICIDX and IDRPICID MUST NOT be present, while the S and E bits
    are unspecified and receivers MUST ignore the values of these
    bits.  The Y bit MUST be identical for all the PACSI NAL units in
    all the RTP sessions carrying the same SVC bitstream.  The Y bit
    MUST be equal to 0 when the parameter packetization-mode is equal
    to 2.
 o  If the T bit is equal to 1, the OPTIONAL field DONC MUST be
    present and specified as below.  Otherwise, the field DONC MUST
    NOT be present.  The field T MUST be equal to 0 if the PACSI NAL
    unit is contained in an STAP-B, MTAP16, MTAP24, or NI-MTAP.

Wenger, et al. Standards Track [Page 39] RFC 6190 RTP Payload Format for SVC May 2011

 o  The A bit MUST be set to 1 if at least one of the remaining NAL
    units in the aggregation packet belongs to an anchor layer
    representation (when the PACSI NAL unit is included in an
    aggregation packet) or if the next non-PACSI NAL unit in
    transmission order belongs to an anchor layer representation (when
    the PACSI NAL unit is included in a single NAL unit packet).
    Otherwise, the A bit MUST be set to 0.
    Informative note: The A bit indicates whether CGS or spatial layer
    switching at a non-IDR layer representation (a layer
    representation with nal_unit_type not equal to 5 and idr_flag not
    equal to 1) can be performed.  With some picture coding structures
    a non-IDR intra layer representation can be used for random
    access.  Compared to using only IDR layer representations, higher
    coding efficiency can be achieved.  The H.264/AVC or SVC solution
    to indicate the random accessibility of a non-IDR intra layer
    representation is using a recovery point SEI message.  The A bit
    offers direct access to this information, without having to parse
    the recovery point SEI message, which may be buried deeply in an
    SEI NAL unit.  Furthermore, the SEI message may or may not be
    present in the bitstream.
 o  The P bit MUST be set to 1 if all the remaining NAL units in the
    aggregation packet have redundant_pic_cnt greater than 0 (when the
    PACSI NAL unit is included in an aggregation packet) or the next
    non-PACSI NAL unit in transmission order has redundant_pic_cnt
    greater than 0 (when the PACSI NAL unit is included in a single
    NAL unit packet).  Otherwise, the P bit MUST be set to 0.
    Informative note: The P bit indicates whether a packet can be
    discarded because it contains only redundant slice NAL units.
    Without this bit, the corresponding information can be obtained
    from the syntax element redundant_pic_cnt, which is contained in
    the variable-length coded slice header.
 o  The C bit MUST be set to 1 if at least one of the remaining NAL
    units in the aggregation packet belongs to an intra layer
    representation (when the PACSI NAL unit is included in an
    aggregation packet) or if the next non-PACSI NAL unit in
    transmission order belongs to an intra layer representation (when
    the PACSI NAL unit is included in a single NAL unit packet).
    Otherwise, the C bit MUST be set to 0.
    Informative note: The C bit indicates whether a packet contains
    intra slices, which may be the only packets to be forwarded, e.g.,
    when the network conditions are particularly adverse.

Wenger, et al. Standards Track [Page 40] RFC 6190 RTP Payload Format for SVC May 2011

 o  The S bit MUST be set to 1, if the first NAL unit following the
    PACSI NAL unit in an aggregation packet is the first VCL NAL unit,
    in decoding order, of a layer representation (when the PACSI NAL
    unit is included in an aggregation packet) or if the next non-
    PACSI NAL unit in transmission order is the first VCL NAL unit, in
    decoding order, of a layer representation(when the PACSI NAL unit
    is included in a single NAL unit packet).  Otherwise, the S bit
    MUST be set to 0.
 o  The E bit MUST be set to 1, if the last NAL unit following the
    PACSI NAL unit in an aggregation packet is the last VCL NAL unit,
    in decoding order, of a layer representation (when the PACSI NAL
    unit is included in an aggregation packet) or if the next non-
    PACSI NAL unit in transmission order is the last VCL NAL unit, in
    decoding order, of a layer representation (when the PACSI NAL unit
    is included in a single NAL unit packet).  Otherwise, the E bit
    MUST be set to 0.
    Informative note: In an aggregation packet it is always possible
    to detect the beginning or end of a layer representation by
    detecting changes in the values of dependency_id, quality_id, and
    temporal_id in NAL unit headers, except from the first and last
    NAL units of a packet.  The S or E bits are used to provide this
    information, for both single NAL unit and aggregation packets, so
    that previous or following packets do not have to be examined.
    This enables MANEs to detect slice loss and take proper action
    such as requesting a retransmission as soon as possible, as well
    as to allow efficient playout buffer handling similarly to the M
    bit present in the RTP header.  The M bit in the RTP header still
    indicates the end of an access unit, not the end of a layer
    representation.
 o  When present, the TL0PICIDX field MUST be set to equal to
    tl0_dep_rep_idx as specified in Annex G of [H.264] for the layer
    representation containing the first NAL unit following the PACSI
    NAL unit in the aggregation packet (when the PACSI NAL unit is
    included in an aggregation packet) or containing the next non-
    PACSI NAL unit in transmission order (when the PACSI NAL unit is
    included in a single NAL unit packet).
 o  When present, the IDRPICID field MUST be set to equal to
    effective_idr_pic_id as specified in Annex G of [H.264] for the
    layer representation containing the first NAL unit following the
    PACSI NAL unit in the aggregation packet (when the PACSI NAL unit
    is included in an aggregation packet) or containing the next non-
    PACSI NAL unit in transmission order (when the PACSI NAL unit is
    included in a single NAL unit packet).

Wenger, et al. Standards Track [Page 41] RFC 6190 RTP Payload Format for SVC May 2011

    Informative note: The TL0PICIDX and IDRPICID fields enable the
    detection of the loss of layer representations in the most
    important temporal layer (with temporal_id equal to 0) by
    receivers as well as MANEs.  SVC provides a solution that uses SEI
    messages, which are harder to parse and may or may not be present
    in the bitstream.  When the PACSI NAL unit is part of an NI-MTAP
    packet, it is possible to infer the correct values of
    tl0_dep_rep_idx and idr_pic_id for all layer representations
    contained in the NI-MTAP by following the rules that specify how
    these parameters are set as given in Annex G of [H.264] and by
    detecting the different layer representations contained in the NI-
    MTAP packet by detecting changes in the values of dependency_id_,
    quality_id, and temporal_id in the NAL unit headers as well as
    using the S and E flags.  The only exception is if NAL units of an
    IDR picture are present in the NI-MTAP in a position other than
    the first NAL unit following the PACSI NAL unit, in which case the
    value of idr_pic_id cannot be inferred.  In this case the NAL unit
    has to be partially parsed to obtain the idr_pic_id.  Note that,
    due to the large size of IDR pictures, their inclusion in an NI-
    MTAP, and especially in a position other than the first NAL unit
    following the PACSI NAL unit, may be neither practical nor useful.
 o  When present, the field DONC indicates the cross-session decoding
    order number (CS-DON) for the first of the remaining NAL units in
    the aggregation packet (when the PACSI NAL unit is included in an
    aggregation packet) or the CS-DON of the next non-PACSI NAL unit
    in transmission order (when the PACSI NAL unit is included in a
    single NAL unit packet).  CS-DON is further discussed in Section
    4.11.
 The PACSI NAL unit MAY include a subset of the SEI NAL units
 associated with the access unit to which the first non-PACSI NAL unit
 in the aggregation packet belongs, and MUST NOT contain SEI NAL units
 associated with any other access unit.
    Informative note:  In H.264/AVC and SVC, within each access unit,
    SEI NAL units must appear before any VCL NAL unit in decoding
    order.  Therefore, without using PACSI NAL units, SEI messages are
    typically only conveyed in the first of the packets carrying an
    access unit.  Senders may repeat SEI NAL units in PACSI NAL units,
    so that they are repeated in more than one packet and thus
    increase robustness against packet losses.  Receivers may use the
    repeated SEI messages in place of missing SEI messages.
 For a PACSI NAL unit included in an aggregation packet, an SEI
 message SHOULD NOT be included in the PACSI NAL unit and also
 included in one of the remaining NAL units contained in the same
 aggregation packet.

Wenger, et al. Standards Track [Page 42] RFC 6190 RTP Payload Format for SVC May 2011

4.10. Empty NAL unit

 An empty NAL unit MAY be included in a single NAL unit packet, an
 STAP-A or an NI-MTAP packet.  Empty NAL units MUST have an RTP
 timestamp (when transported in a single NAL unit packet) or NALU-
 time (when transported in an aggregation packet) that is associated
 with an access unit for which there exists at least one NAL unit of
 type 1, 5, or 20.  When MST is used, the type 1, 5, or 20 NAL unit
 may be in a different RTP session.  Empty NAL units may be used in
 the decoding order recovery process of the NI-T mode as described in
 Section 5.2.1.
 The packet structure is shown in the following figure.
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |F|NRI|  Type   | Subtype |J|K|L|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure 4.  Empty NAL unit structure.
 The fields MUST be set as follows:
   F MUST be equal to 0
   NRI MUST be equal to 3
   Type MUST be equal to 31
   Subtype MUST be equal to 1
   J MUST be equal to 0
   K MUST be equal to 0
   L MUST be equal to 0

4.11. Decoding Order Number (DON)

 The DON concept is introduced in [RFC6184] and is used to recover the
 decoding order when interleaving is used within a single session.
 Section 5.5 of [RFC6184] applies when using SST.
 When using MST, it is necessary to recover the decoding order across
 the various RTP sessions regardless if interleaving is used or not.
 In addition to the timestamp mechanism described later, the CS-DON
 mechanism is an extension of the DON facility that can be used for
 this purpose, and is defined in the following section.

4.11.1. Cross-Session DON (CS-DON) for Multi-Session Transmission

 The cross-session decoding order number (CS-DON) is a number that
 indicates the decoding order of NAL units across all RTP sessions
 involved in MST.  It is similar to the DON concept in [RFC6184], but
 contrary to [RFC6184] where the DON was used only for interleaved

Wenger, et al. Standards Track [Page 43] RFC 6190 RTP Payload Format for SVC May 2011

 packetization, in this memo it is used not only in the interleaved
 MST mode (I-C) but also in two of the non-interleaved MST modes (NI-C
 and NI-TC).
 When the NI-C or NI-TC MST modes are in use, the packetization of
 each session MUST be as specified in Section 5.2.2.  In PACSI NAL
 units the CS-DON value is explicitly coded in the field DONC.  For
 non-PACSI NAL units the CS-DON value is derived as follows.  Let SN
 indicate the RTP sequence number of a packet.
 o  For each non-PACSI NAL unit carried in a session using the single
    NAL unit session packetization mode, the CS-DON value of the NAL
    unit is equal to (DONC_prev_PACSI + SN_diff - 1) % 65536, wherein
    "%" is the modulo operation, DONC_prev_PACSI is the DONC value of
    the previous PACSI NAL unit with the same NALU-time as the current
    NAL unit, and SN_diff is calculated as follows:
       if SN1 > SN2, SN_diff = SN1 - SN2
       else SN_diff = SN2 + 65536 - SN1
    where SN1 and SN2 are the SNs of the current NAL unit and the
    previous PACSI NAL unit with the same NALU-time, respectively.
 o  For non-PACSI NAL units carried in a session using the non-
    interleaved session packetization mode, the CS-DON value of each
    non-PACSI NAL unit is derived as follows.
       For a non-PACSI NAL unit in a single NAL unit packet, the
       following applies.
          If the previous PACSI NAL unit is contained in a single NAL
          unit packet, the CS-DON value of the NAL unit is calculated
          as above;
          otherwise (the previous PACSI NAL unit is contained in an
          STAP-A packet), the CS-DON value of the NAL unit is
          calculated as above, with DONC_prev_PACSI being replaced by
          the CS-DON value of the previous non-PACSI NAL unit in
          decoding order (i.e., the CS-DON value of the last NAL unit
          of the STAP-A packet).
       For a non-PACSI NAL unit in an STAP-A packet, the following
       applies.
          If the non-PACSI NAL unit is the first non-PACSI NAL unit in
          the STAP-A packet, the CS-DON value of the NAL unit is equal
          to DONC of the PACSI NAL unit in the STAP-A packet;

Wenger, et al. Standards Track [Page 44] RFC 6190 RTP Payload Format for SVC May 2011

          otherwise (the non-PACSI NAL unit is not the first non-
          PACSI NAL unit in the STAP-A packet), the CS-DON value of
          the NAL unit is equal to: (the CS-DON value of the previous
          non-PACSI NAL unit in decoding order + 1) % 65536, wherein
          "%" is the modulo operation.
       For a non-PACSI NAL unit in a number of FU-A packets, the CS-
       DON value of the NAL unit is calculated the same way as when
       the single NAL unit session packetization mode is in use, with
       SN1 being the SN value of the first FU-A packet.
       For a non-PACSI NAL unit in an NI-MTAP packet, the CS-DON value
       is equal to the value of the DON field of the non-interleaved
       multi-time aggregation unit.
 When the I-C MST packetization mode is in use, the DON values derived
 according to [RFC6184] for all the NAL units in each of the RTP
 sessions MUST indicate CS-DON values.

5. Packetization Rules

 Section 6 of [RFC6184] applies in this memo, with the following
 additions.

5.1. Packetization Rules for Single-Session Transmission

 All receivers MUST support the single NAL unit packetization mode to
 provide backward compatibility to endpoints supporting only the
 single NAL unit mode of [RFC6184].  However, the use of single NAL
 unit packetization mode (packetization-mode equal to 0) SHOULD be
 avoided whenever possible, because encapsulating NAL units of small
 sizes in their own packets (e.g., small NAL units containing
 parameter sets, prefix NAL units, or SEI messages) is less efficient
 due to the packet header overhead.
 All receivers MUST support the non-interleaved mode.
    Informative note: The non-interleaved mode of [RFC6184] does allow
    an application to encapsulate a single NAL unit in a single RTP
    packet.  Historically, the single NAL unit mode has been included
    in [RFC6184] only for compatibility with ITU-T Rec. H.241 Annex A
    [H.241].  There is no point in carrying this historic ballast
    towards a new application space such as the one provided with SVC.
    The implementation complexity increase for supporting the
    additional mechanisms of the non-interleaved mode (namely, STAP-A
    and FU-A) is minor, whereas the benefits are significant.  As a
    result, the support of STAP-A and FU-A is required.  Additionally,

Wenger, et al. Standards Track [Page 45] RFC 6190 RTP Payload Format for SVC May 2011

    support for two of the three NAL unit types defined in this memo,
    namely, empty NAL units and NI-MTAP is needed, as specified in
    Section 4.5.1.
 A NAL unit of small size SHOULD be encapsulated in an aggregation
 packet together with one or more other NAL units.  For example, non-
 VCL NAL units such as access unit delimiters, parameter sets, or SEI
 NAL units are typically small.
 A prefix NAL unit and the NAL unit with which it is associated, and
 which follows the prefix NAL unit in decoding order, SHOULD be
 included in the same aggregation packet whenever an aggregation
 packet is used for the associated NAL unit, unless this would violate
 session MTU constraints or if fragmentation units are used for the
 associated NAL unit.
    Informative note: Although the prefix NAL unit is ignored by an
    H.264/AVC decoder, it is necessary in the SVC decoding process.
    Given the small size of the prefix NAL unit, it is best if it is
    transported in the same RTP packet as its associated NAL unit.
 When only an H.264/AVC compatible subset of the SVC base layer is
 transmitted in an RTP session, the subset MUST be encapsulated
 according to [RFC6184].  This way, an [RFC6184] receiver will be able
 to receive the H.264/AVC compatible bitstream subset.
 When a set of layers including one or more SVC enhancement layers is
 transmitted in an RTP session, the set SHOULD be carried in one RTP
 stream that SHOULD be encapsulated according to this memo.

5.2. Packetization Rules for Multi-Session Transmission

 When MST is used, the packetization rules specified in Section 5.1
 still apply.  In addition, the following packetization rules MUST be
 followed, to ensure that decoding order of NAL units carried in the
 sessions can be correctly recovered for each of the MST packetization
 modes using the de-packetization process specified in Section 6.2.
 The NI-T and NI-TC modes both use timestamps to recover the decoding
 order.  In order to be able to do so, it is necessary for the RTP
 packet stream to contain data for all sampling instances of a given
 RTP session in all enhancement RTP sessions that depend on the given
 RTP session.  The NI-C and I-C modes do not have this limitation, and
 use the CS-DON values as a means to explicitly indicate decoding
 order, either directly coded in PACSI NAL units, or inferred from

Wenger, et al. Standards Track [Page 46] RFC 6190 RTP Payload Format for SVC May 2011

 them using the packetization rules.  It is noted that the NI-TC mode
 offers both alternatives and it is up to the receiver to select which
 one to use.

5.2.1. NI-T/NI-TC Packetization Rules

 When using the NI-T mode and a PACSI NAL unit is present, the T bit
 MUST be equal to 0, i.e., the DONC field MUST NOT be present.
 When using the NI-T mode, the optional parameters sprop-mst-remux-
 buf-size, sprop-remux-buf-req, remux-buf-cap, sprop-remux-init-buf-
 time, sprop-mst-max-don-diff MUST NOT be present.
 When the NI-T or NI-TC MST mode is in use, the following applies.
 If one or more NAL units of an access unit of sampling time instance
 t is present in RTP session A, then one or more NAL units of the same
 access unit MUST be present in any enhancement RTP session that
 depends on RTP session A.
    Informative note: The mapping between RTP and NTP format
    timestamps is conveyed in RTCP SR packets.  In addition, the
    mechanisms for faster media timestamp synchronization discussed in
    [RFC6051] may be used to speed up the acquisition of the RTP-to-
    wall-clock mapping.
    Informative note: The rule above may require the insertion of NAL
    units, typically when temporal scalability is used, i.e., an
    enhancement RTP session does not contain any NAL units for an
    access unit with a particular NTP timestamp (media timestamp),
    which, however, is present in a lower enhancement RTP session or
    the base RTP session.  There are two ways to insert additional NAL
    units in order to satisfy this rule:
  1. One option for adding additional NAL units is to use empty NAL

units (defined in Section 4.10), which can be used by the

      process described in Section 6.2.1 for the access unit
      reordering process.
  1. Additional NAL units may also be added by the encoder itself,

for example, by transmitting coded data that simply instruct the

      decoder to repeat the previous picture.  This option, however,
      may be difficult to use with pre-encoded content.
 If a packet must be inserted in order to satisfy the above rule,
 e.g., in case of a MANE generating multiple RTP streams out of a
 single RTP stream, the inserted packet must have an RTP timestamp
 that maps to the same wall-clock time (in NTP format) as the one of

Wenger, et al. Standards Track [Page 47] RFC 6190 RTP Payload Format for SVC May 2011

 the RTP timestamp of any packet of the access unit present in any
 lower enhancement RTP session or the base RTP session.  This is easy
 to accomplish if the NAL unit or the packet can be inserted at the
 time of the RTP stream generation, since the media timestamp (NTP
 timestamp) must be the same for the inserted packet and the packet of
 the corresponding access unit.  If there is no knowledge of the media
 time at RTP stream generation or if the RTP streams are not generated
 at the same instance, this can be also applied later in the
 transmission process.  In this case the NTP timestamp of the inserted
 packet can be calculated as follows.
 Assume that a packet A2 of an access unit with RTP timestamp TS_A2 is
 present in base RTP session A, and that no packet of that access unit
 is present in enhancement RTP session B, as shown in Figure 5.  Thus,
 a packet B2 must be inserted into session B following the rule above.
 The most recent RTCP sender report in session A carries NTP timestamp
 NTP_A and the RTP timestamp TS_A.  The sender report in session B
 with a lower NTP timestamp than NTP_A is NTP_B, and carries the RTP
 timestamp TS_B.
   RTP  session B:..B0........B1........(B2)......................
   RTCP session B:.....SR(NTP_B,TS_B).............................
   RTP  session A:..A0........A1........A2........................
   RTCP session A:..................SR(NTP_A,TS_A)................
  1. —————-|–x——|—–x—|————————>

NTP time

  1. ——————-+←———>+↔+————————>

t1 t2 RTP TS(B) time

 Figure 5.  Example calculation of RTP timestamp for packet
 insertion in an enhancement layer RTP session
 The vertical bars ("|")in the NTP time line in the figure above
 indicate that access unit data is present in at least one of the
 sessions.  The "x" marks indicate the times of the sender reports.
 The RTP timestamp time line for session B, shown right below the NTP
 time line, indicates two time segments, t1 and t2. t1 is the time
 difference between the sender reports between the two sessions,
 expressed in RTP timestamp clock ticks, and t2 is the time difference
 from the session A sender report to the A2 packet, again expressed in
 RTP timestamp clock ticks.  The sum of these differences is added to

Wenger, et al. Standards Track [Page 48] RFC 6190 RTP Payload Format for SVC May 2011

 the RTP timestamp of the session report from session B in order to
 derive the correct RTP timestamp for the inserted packet B2.  In
 other words:
   TS_B2 = TS_B + t1 + t2
 Let toRTP() be a function that calculates the RTP time difference (in
 clock ticks of the used clock) given an NTP timestamp difference, and
 effRTPdiff() be a function that calculates the effective difference
 between two timestamps, including wraparounds:
   effRTPdiff( ts1, ts2 ):
       if( ts1 <= ts2 ) then
           effRTPdiff := ts1-ts2
       else
           effRTPDiff := (4294967296 + ts2) - ts1
 We have:
   t1 = toRTP(NTP_A - NTP_B) and t2 = effRTPdiff(TS_A2, TS_A)
 Hence in order to generate the RTP timestamp TS_B2 for the inserted
 packet B2, the RTP timestamp for packet B2 TS_B2 can be calculated as
 follows.
   TS_B2 =  TS_B + toRTP(NTP_A - NTP_B) +  effRTPdiff(TS_A2, TS_A)

5.2.2. NI-C/NI-TC Packetization Rules

 When the NI-C or NI-TC MST mode is in use, the following applies for
 each of the RTP sessions.
 o  For each single NAL unit packet containing a non-PACSI NAL unit,
    the previous packet, if present, MUST have the same RTP timestamp
    as the single NAL unit packet, and the following applies.
    o  If the NALU-time of the non-PACSI NAL unit is not equal to the
       NALU-time of the previous non-PACSI NAL unit in decoding order,
       the previous packet MUST contain a PACSI NAL unit containing
       the DONC field.
 o  In an STAP-A packet the first NAL unit in the STAP-A packet MUST
    be a PACSI NAL unit containing the DONC field.
 o  For an FU-A packet the previous packet MUST have the same RTP
    timestamp as the FU-A packet, and the following applies.

Wenger, et al. Standards Track [Page 49] RFC 6190 RTP Payload Format for SVC May 2011

    o If the FU-A packet is the start of the fragmented NAL unit, the
       following applies.
       o  If the NALU-time of the fragmented NAL unit is not equal to
          the NALU-time of the previous non-PACSI NAL unit in decoding
          order, the previous packet MUST contain a PACSI NAL unit
          containing the DONC field;
       o  Otherwise, (the NALU-time of the fragmented NAL unit is
          equal to the NALU-time of the previous non-PACSI NAL unit in
          decoding order), the previous packet MAY contain a PACSI NAL
          unit containing the DONC field.
    o  Otherwise, if the FU-A packet is the end of the fragmented NAL
       unit, the following applies.
       o  If the next non-PACSI NAL unit in decoding order has NALU-
          time equal to the NALU-time of the fragmented NAL unit, and
          is carried in a number of FU-A packets or a single NAL unit
          packet, the next packet MUST be a single NAL unit packet
          containing a PACSI NAL unit containing the DONC field.
       o  Otherwise (the FU-A packet is neither the start nor the end
          of the fragmented NAL unit), the previous packet MUST be a
          FU-A packet.
 o  For each single NAL unit packet containing a PACSI NAL unit, if
    present, the PACSI NAL unit MUST contain the DONC field.
 o  When the optional media type parameter sprop-mst-csdon-always-
    present is equal to 1, the session packetization mode in use MUST
    be the non-interleaved mode, and only STAP-A and NI-MTAP packets
    can be used.

5.2.3. I-C Packetization Rules

 When the I-C MST packetization mode is in use, the following applies.
 o  When a PACSI NAL unit is present, the T bit MUST be equal to 0,
    i.e., the DONC field is not present, and the Y bit MUST be equal
    to 0, i.e., the TL0PICIDX and IDRPICID are not present.

5.2.4. Packetization Rules for Non-VCL NAL Units

 NAL units that do not directly encode video slices are known in H.264
 as non-VCL NAL units.  Non-VCL units that are only used by, or only
 relevant to, enhancement RTP sessions SHOULD be sent in the lowest
 session to which they are relevant.

Wenger, et al. Standards Track [Page 50] RFC 6190 RTP Payload Format for SVC May 2011

 Some senders, however, such as those sending pre-encoded data, may be
 unable to easily determine which non-VCL units are relevant to which
 session.  Thus, non-VCL NAL units MAY, instead, be sent in a session
 on which the session using these non-VCL NAL units depends (e.g., the
 base RTP session).
 If a non-VCL unit is relevant to more than one RTP session, neither
 of which depends on the other(s), the NAL unit MAY be sent in another
 session on which all these sessions depend.

5.2.5. Packetization Rules for Prefix NAL Units

 Section 5.1 of this memo applies, with the following addition.  If
 the base layer is sent in a base RTP session using [RFC6184], prefix
 NAL units MAY be sent in the lowest enhancement RTP session rather
 than in the base RTP session.

6. De-Packetization Process

6.1. De-Packetization Process for Single-Session Transmission

 For single-session transmission, where a single RTP session is used,
 the de-packetization process specified in Section 7 of [RFC6184]
 applies.

6.2. De-Packetization Process for Multi-Session Transmission

 For multi-session transmission, where more than one RTP session is
 used to receive data from the same SVC bitstream, the de-
 packetization process is specified as follows.
 As for a single RTP session, the general concept behind the de-
 packetization process is to reorder NAL units from transmission order
 to the NAL unit decoding order.
 The sessions to be received MUST be identified by mechanisms
 specified in Section 7.2.3.  An enhancement RTP session typically
 contains an RTP stream that depends on at least one other RTP
 session, as indicated by mechanisms defined in Section 7.2.3.  A
 lower RTP session to an enhancement RTP session is an RTP session on
 which the enhancement RTP session depends.  The lowest RTP session
 for a receiver is the base RTP session, which does not depend on any
 other RTP session received by the receiver.  The highest RTP session
 for a receiver is the RTP session on which no other RTP session
 received by the receiver depends.

Wenger, et al. Standards Track [Page 51] RFC 6190 RTP Payload Format for SVC May 2011

 For each of the RTP sessions, the RTP reception process as specified
 in RFC 3550 is applied.  Then the received packets are passed into
 the payload de-packetization process as defined in this memo.
 The decoding order of the NAL units carried in all the associated RTP
 sessions is then recovered by applying one of the following
 subsections, depending on which of the MST packetization modes is in
 use.

6.2.1. Decoding Order Recovery for the NI-T and NI-TC Modes

 The following process MUST be applied when the NI-T packetization
 mode is in use.  The following process MAY be applied when the NI-TC
 packetization mode is in use.
 The process is based on RTP session dependency signaling, RTP
 sequence numbers, and timestamps.
 The decoding order of NAL units within an RTP packet stream in RTP
 session is given by the ordering of sequence numbers SN of the RTP
 packets that contain the NAL units, and the order of appearance of
 NAL units within a packet.
 Timing information according to the media timestamp TS, i.e., the NTP
 timestamp as derived from the RTP timestamp of an RTP packet, is
 associated with all NAL units contained in the same RTP packet
 received in an RTP session.
 For NI-MTAP packets the NALU-time is derived for each contained NAL
 unit by using the "TS offset" value in the NI-MTAP packet as defined
 in Section 4.10, and is used instead of the RTP packet timestamp to
 derive the media timestamp, e.g., using the NTP wall clock as
 provided via RTCP sender reports.  NAL units contained in
 fragmentation packets are handled as defragmented, entire NAL units
 with their own media timestamps.  All NAL units associated with the
 same value of media timestamp TS are part of the same access unit
 AU(TS).  Any empty NAL units SHOULD be kept as, effectively, access
 unit indicators in the reordering process.  Empty NAL units and PACSI
 NAL units SHOULD be removed before passing access unit data to the
 decoder.
    Informative note: These empty NAL units are used to associate NAL
    units present in other RTP sessions with RTP sessions not
    containing any data for an access unit of a particular time
    instance.  They act as access unit indicators in sessions that
    would otherwise contain no data for the particular access unit.
    The presence of these NAL units is ensured by the packetization
    rules in Section 5.2.1.

Wenger, et al. Standards Track [Page 52] RFC 6190 RTP Payload Format for SVC May 2011

 It is assumed that the receiver has established an operation point
 (DID, QID, and TID values), and has identified the highest
 enhancement RTP session for this operation point.  The decoding order
 of NAL units from multiple RTP streams in multiple RTP sessions MUST
 be recovered into a single sequence of NAL units, grouped into access
 units, by performing any process equivalent to the following steps.
 The general process is described in Section 4.2 of [RFC6051].  For
 convenience the instructions of [RFC6051] are repeated and applied to
 NAL units rather than to full RTP packets.  Additionally, SVC-
 specific extensions to the procedure in Section 4.2.  of [RFC6051]
 are presented in the following list:
    o  The process should be started with the NAL units received in
       the highest RTP session with the first media timestamp TS (in
       NTP format) available in the session's (de-jittering) buffer.
       It is assumed that packets in the de-jittering buffer are
       already stored in RTP sequence number order.
    o  Collect all NAL units associated with the same value of media
       timestamp TS, starting from the highest RTP session, from all
       the (de-jittering) buffers of the received RTP sessions.  The
       collected NAL units will be those associated with the access
       unit AU(TS).
    o  Place the collected NAL units in the order of session
       dependency as derived by the dependency indication as specified
       in Section 7.2.3, starting from the lowest RTP session.
    o  Place the session ordered NAL units in decoding order within
       the particular access unit by satisfying the NAL unit ordering
       rules for SVC access units, as described in the informative
       algorithm provided in Section 6.2.1.1.
    o  Remove NI-MTAP and any PACSI NAL units from the access unit
       AU(TS).
    o  The access units can then be transferred to the decoder.
       Access units AU(TS) are transferred to the decoder in the order
       of appearance (given by the order of RTP sequence numbers) of
       media timestamp values TS in the highest RTP session associated
       with access unit AU(TS).
          Informative note: Due to packet loss it is possible that not
          all sessions may have NAL units present for the media
          timestamp value TS present in the highest RTP session.  In
          such a case, an algorithm may: a) proceed to the next
          complete access unit with NAL units present in all the
          received RTP sessions; or b) consider a new highest RTP

Wenger, et al. Standards Track [Page 53] RFC 6190 RTP Payload Format for SVC May 2011

          session, the highest RTP session for which the access unit
          is complete, and apply the process above.  The algorithm may
          return to the original highest RTP session when a complete
          and error-free access unit that contains NAL units in all
          the sessions is received.
 The following gives an informative example.
 The example shown in Figure 6 refers to three RTP sessions A, B, and
 C containing an SVC bitstream transmitted as 3 sources.  In the
 example, the dependency signaling (described in Section 7.2.3)
 indicates that session A is the base RTP session, B is the first
 enhancement RTP session and depends on A, and C is the second
 enhancement RTP session and depends on A and B.  A hierarchical
 picture coding prediction structure is used, in which session A has
 the lowest frame rate and sessions B and C have the same but higher
 frame rate.
 The figure shows NAL units contained in RTP packets that are stored
 in the de-jittering buffer at the receiver for session de-
 packetization.  The NAL units are already reordered according to
 their RTP sequence number order and, if within an aggregation packet,
 according to the order of their appearance within the aggregation
 packet.  The figure indicates for the received NAL units the decoding
 order within the sessions, as well as the associated media (NTP)
 timestamps ("TS[..]").  NAL units of the same access unit within a
 session are grouped by "(.,.)" and share the same media timestamp TS,
 which is shown at the bottom of the figure.  Note that the timestamps
 are not in increasing order since, in this example, the decoding
 order is different from the output/display order.
 The process first proceeds to the NAL units associated with the first
 media timestamp TS[1] present in the highest session C and
 removes/ignores all preceding (in decoding order) NAL units to NAL
 units with TS[1] in each of the de-jittering buffers of RTP sessions
 A, B, and C.  Then, starting from session C, the first media
 timestamp available in decoding order (TS[1]) is selected and NAL
 units starting from RTP session A, and sessions B and C are placed in
 order of the RTP session dependency as required by Section 7.2.3 of
 this memo (in the example for TS[1]: first session B and then session
 C) into the access unit AU(TS[1]) associated with media timestamp
 TS[1].  Then the next media timestamp TS[3] in order of appearance in
 the highest RTP session C is processed and the process described
 above is repeated.  Note that there may be access units with no NAL
 units present, e.g., in the lowest RTP session A (see, e.g., TS[1]).
 With TS[8], the first access unit with NAL units present in all the
 RTP sessions appears in the buffers.

Wenger, et al. Standards Track [Page 54] RFC 6190 RTP Payload Format for SVC May 2011

 C: ------------(1,2)-(3,4)--(5)---(6)---(7,8)(9,10)-(11)--(12)----
      |     |     |     |     |     |      |    |     |      |
 B: -(1,2)-(3,4)-(5)---(6)--(7,8)-(9,10)-(11)-(12)--(13,14)(15,15)-
      |     |                 |     |                 |      |
 A: -------(1)---------------(2)---(3)---------------(4)----(5)----
 ---------------------------------------------------decoding order-->
 TS: [4]   [2]   [1]   [3]   [8]   [6]   [5]   [7]   [12]   [10]
 Key:
 A, B, C                - RTP sessions
 Integer values in "()" - NAL unit decoding order within RTP session
 "( )"                  - groups the NAL units of an access unit
                          in an RTP session
 "|"                    - indicates corresponding NAL units of the
                          same access unit AU(TS[..]) in the RTP
                          sessions
 Integer values in "[]" - media timestamp TS, sampling time
                          as derived, e.g., from NTP timestamp
                          associated with the access unit AU(TS[..]),
                          consisting of NAL units in the sessions
                          above each TS value.
 Figure 6.  Example of decoding order recovery in multi-source
 transmission.

6.2.1.1. Informative Algorithm for NI-T Decoding Order Recovery within

        an Access Unit
 Within an access unit, the [H.264] specification (Sections 7.4.1.2.3
 and G.7.4.1.2.3) constrains the valid decoding order of NAL units.
 These constraints make it possible to reconstruct a valid decoding
 order for the NAL units of an access unit based only on the order of
 NAL units in each session, the NAL unit headers, and Supplemental
 Enhancement Information message headers.
 This section specifies an informative algorithm to reconstruct a
 valid decoding order for NAL units within an access unit.  Other NAL
 unit orderings may also be valid; however, any compliant NAL unit
 ordering will describe the same video stream and ancillary data as
 the one produced by this algorithm.
 An actual implementation, of course, needs only to behave "as if"
 this reordering is done.  In particular, NAL units that are discarded
 by an implementation's decoding process do not need to be reordered.

Wenger, et al. Standards Track [Page 55] RFC 6190 RTP Payload Format for SVC May 2011

 In this algorithm, NAL units within an access unit are first ordered
 by NAL unit type, in the order specified in Table 12 below, except
 from NAL unit type 14, which is handled specially as described in the
 table.  NAL units of the same type are then ordered as specified for
 the type, if necessary.
 For the purposes of this algorithm, "session order" is the order of
 NAL units implied by their transmission order within an RTP session.
 For the non-interleaved and single NAL unit modes, this is the RTP
 sequence number order coupled with the order of NAL units within an
 aggregation unit.
 Table 12.  Ordering of NAL unit types within an Access Unit
  Type    Description / Comments
 -----------------------------------------------------------
   9      Access unit delimiter
   7      Sequence parameter set
   13     Sequence parameter set extension
   15     Subset sequence parameter set
   8      Picture parameter set
   16-18  Reserved
   6      Supplemental enhancement information (SEI)
          If an SEI message with a first payload of 0 (Buffering
          Period) is present, it must be the first SEI message.
          If SEI messages with a Scalable Nesting (30) payload and
          a nested payload of 0 (Buffering Period) are present,
          these then follow the first SEI message.  Such an SEI
          message with the all_layer_representations_in_au_flag
          equal to 1 is placed first, followed by any others,
          sorted in increasing order of DQId.
          All other SEI messages follow in any order.
   14     Prefix NAL unit in scalable extension
   1      Coded slice of a non-IDR picture
   5      Coded slice of an IDR picture

Wenger, et al. Standards Track [Page 56] RFC 6190 RTP Payload Format for SVC May 2011

          NAL units of type 1 or 5 will be sent within only a
          single session for any given access unit.  They are
          placed in session order.  (Note: Any given access unit
          will contain only NAL units of type 1 or type 5, not
          both.)
          If NAL units of type 14 are present, every NAL unit of
          type 1 or 5 is prefixed by a NAL unit of type 14.  (Note:
          Within an access unit, every NAL unit of type 14 is
          identical, so correlation of type 14 NAL units with the
          other NAL units is not necessary.)
   12     Filler data
          The only restriction of filler data NAL units within an
          access unit is that they shall not precede the first VCL
          NAL unit with the same access unit.
   19     Coded slice of an auxiliary coded picture without
          partitioning
          These NAL units will be sent within only a single
          session for any given access unit, and are placed in
          session order.
    20    Coded slice in scalable extension
    21-23 Reserved
          Type 20 NAL units are placed in increasing order of DQId.
          Within each DQId value, they are placed in session order.
          (Note: SVC slices with a given DQId value will be sent
          within only a single session for any given access unit.)
          Type 21-23 NAL units are placed immediately following
          the non-reserved-type VCL NAL unit they follow in
          session order.
   10     End of sequence
   11     End of stream

6.2.2. Decoding Order Recovery for the NI-C, NI-TC, and I-C Modes

 The following process MUST be used when either the NI-C or I-C MST
 packetization mode is in use.  The following process MAY be applied
 when the NI-TC MST packetization mode is in use.

Wenger, et al. Standards Track [Page 57] RFC 6190 RTP Payload Format for SVC May 2011

 The RTP packets output from the RTP-level reception processing for
 each session are placed into a re-multiplexing buffer.
 It is RECOMMENDED to set the size of the re-multiplexing buffer (in
 bytes) equal to or greater than the value of the sprop-remux-buf-req
 media type parameter of the highest RTP session the receiver
 receives.
 The CS-DON value is calculated and stored for each NAL unit.
    Informative note: The CS-DON value of a NAL unit may rely on
    information carried in another packet than the packet containing
    the NAL unit.  This happens, e.g., when the CS-DON values need to
    be derived for non-PACSI NAL units contained in single NAL unit
    packets, as the single NAL unit packets themselves do not contain
    CS-DON information.  In this case, when no packet containing
    required CS-DON information is received for a NAL unit, this NAL
    unit has to be discarded by the receiver as it cannot be fed to
    the decoder in the correct order.  When the optional media type
    parameter sprop-mst-csdon-always-present is equal to 1, no such
    dependency exists, i.e., the CS-DON value of any particular NAL
    unit can be derived solely according to information in the packet
    containing the NAL unit, and therefore, the receiver does not need
    to discard any received NAL units.
 The receiver operation is described below with the help of the
 following functions and constants:
 o  Function AbsDON is specified in Section 8.1 of [RFC6184].
 o  Function don_diff is specified in Section 5.5 of [RFC6184].
 o  Constant N is the value of the OPTIONAL sprop-mst-remux-buf-size
    media type parameter of the highest RTP session incremented by 1.
 Initial buffering lasts until one of the following conditions is
 fulfilled:
 o  There are N or more VCL NAL units in the re-multiplexing buffer.
 o  If sprop-mst-max-don-diff of the highest RTP session is present,
    don_diff(m,n) is greater than the value of sprop-mst-max-don-diff
    of the highest RTP session, where n corresponds to the NAL unit
    having the greatest value of AbsDON among the received NAL units
    and m corresponds to the NAL unit having the smallest value of
    AbsDON among the received NAL units.

Wenger, et al. Standards Track [Page 58] RFC 6190 RTP Payload Format for SVC May 2011

 o  Initial buffering has lasted for the duration equal to or greater
    than the value of the OPTIONAL sprop-remux-init-buf-time media
    type parameter of the highest RTP session.
 The NAL units to be removed from the re-multiplexing buffer are
 determined as follows:
 o  If the re-multiplexing buffer contains at least N VCL NAL units,
    NAL units are removed from the re-multiplexing buffer and passed
    to the decoder in the order specified below until the buffer
    contains N-1 VCL NAL units.
 o  If sprop-mst-max-don-diff of the highest RTP session is present,
    all NAL units m for which don_diff(m,n) is greater than sprop-
    max-don-diff of the highest RTP session are removed from the re-
    multiplexing buffer and passed to the decoder in the order
    specified below.  Herein, n corresponds to the NAL unit having the
    greatest value of AbsDON among the NAL units in the re-
    multiplexing buffer.
 The order in which NAL units are passed to the decoder is specified
 as follows:
 o  Let PDON be a variable that is initialized to 0 at the beginning
    of the RTP sessions.
 o  For each NAL unit associated with a value of CS-DON, a CS-DON
    distance is calculated as follows.  If the value of CS-DON of the
    NAL unit is larger than the value of PDON, the CS-DON distance is
    equal to CS-DON - PDON.  Otherwise, the CS-DON distance is equal
    to 65535 - PDON + CS-DON + 1.
 o  NAL units are delivered to the decoder in increasing order of CS-
    DON distance.  If several NAL units share the same value of CS-
    DON distance, they can be passed to the decoder in any order.
 o  When a desired number of NAL units have been passed to the
    decoder, the value of PDON is set to the value of CS-DON for the
    last NAL unit passed to the decoder.

7. Payload Format Parameters

 This section specifies the parameters that MAY be used to select
 optional features of the payload format and certain features of the
 bitstream.  The parameters are specified here as part of the media
 type registration for the SVC codec.  A mapping of the parameters
 into the Session Description Protocol (SDP) [RFC4566] is also

Wenger, et al. Standards Track [Page 59] RFC 6190 RTP Payload Format for SVC May 2011

 provided for applications that use SDP.  Equivalent parameters could
 be defined elsewhere for use with control protocols that do not use
 SDP.
 Some parameters provide a receiver with the properties of the stream
 that will be sent.  The names of all these parameters start with
 "sprop" for stream properties.  Some of these "sprop" parameters are
 limited by other payload or codec configuration parameters.  For
 example, the sprop-parameter-sets parameter is constrained by the
 profile-level-id parameter.  The media sender selects all "sprop"
 parameters rather than the receiver.  This uncommon characteristic of
 the "sprop" parameters may be incompatible with some signaling
 protocol concepts, in which case the use of these parameters SHOULD
 be avoided.

7.1. Media Type Registration

 The media subtype for the SVC codec has been allocated from the IETF
 tree.
 The receiver MUST ignore any unspecified parameter.
    Informative note: Requiring that the receiver ignore unspecified
    parameters allows for backward compatibility of future extensions.
    For example, if a future specification that is backward compatible
    to this specification specifies some new parameters, then a
    receiver according to this specification is capable of receiving
    data per the new payload but ignoring those parameters newly
    specified in the new payload specification.  This provision is
    also present in [RFC6184].
 Media Type name:     video
 Media subtype name:  H264-SVC
 Required parameters: none
 OPTIONAL parameters:
    In the following definitions of parameters, "the stream" or "the
    NAL unit stream" refers to all NAL units conveyed in the current
    RTP session in SST, and all NAL units conveyed in the current RTP
    session and all NAL units conveyed in other RTP sessions that the
    current RTP session depends on in MST.

Wenger, et al. Standards Track [Page 60] RFC 6190 RTP Payload Format for SVC May 2011

    profile-level-id:
       A base16 [RFC4648] (hexadecimal) representation of the
       following three bytes in the sequence parameter set or subset
       sequence parameter set NAL unit specified in [H.264]: 1)
       profile_idc; 2) a byte herein referred to as profile-iop,
       composed of the values of constraint_set0_flag,
       constraint_set1_flag, constraint_set2_flag,
       constraint_set3_flag, constraint_set4_flag,
       constraint_set5_flag, and reserved_zero_2bits, in bit-
       significance order, starting from the most-significant bit, and
       3) level_idc.  Note that reserved_zero_2bits is required to be
       equal to 0 in [H.264], but other values for it may be specified
       in the future by ITU-T or ISO/IEC.
       The profile-level-id parameter indicates the default sub-
       profile, i.e., the subset of coding tools that may have been
       used to generate the stream or that the receiver supports, and
       the default level of the stream or the one that the receiver
       supports.
       The default sub-profile is indicated collectively by the
       profile_idc byte and some fields in the profile-iop byte.
       Depending on the values of the fields in the profile-iop byte,
       the default sub-profile may be the same set of coding tools
       supported by one profile, or a common subset of coding tools of
       multiple profiles, as specified in Subsection G.7.4.2.1.1 of
       [H.264].  The default level is indicated by the level_idc byte,
       and, when profile_idc is equal to 66, 77, or 88 (the Baseline,
       Main, or Extended profile) and level_idc is equal to 11,
       additionally by bit 4 (constraint_set3_flag) of the profile-iop
       byte.  When profile_idc is equal to 66, 77, or 88 (the
       Baseline, Main, or Extended profile) and level_idc is equal to
       11, and bit 4 (constraint_set3_flag) of the profile-iop byte is
       equal to 1, the default level is Level 1b.
       Table 13 lists all profiles defined in Annexes A and G of
       [H.264] and, for each of the profiles, the possible
       combinations of profile_idc and profile-iop that represent the
       same sub-profile.
       Table 13.  Combinations of profile_idc and profile-iop
       representing the same sub-profile corresponding to the full set
       of coding tools supported by one profile.  In the following, x
       may be either 0 or 1, while the profile names are indicated as
       follows.  CB: Constrained Baseline profile, B: Baseline
       profile, M: Main profile, E: Extended profile, H: High profile,
       H10: High 10 profile, H42: High 4:2:2 profile, H44: High 4:4:4
       Predictive profile, H10I: High 10 Intra profile, H42I: High

Wenger, et al. Standards Track [Page 61] RFC 6190 RTP Payload Format for SVC May 2011

       4:2:2 Intra profile, H44I: High 4:4:4 Intra profile, C44I:
       CAVLC 4:4:4 Intra profile, SB: Scalable Baseline profile, SH:
       Scalable High profile, and SHI: Scalable High Intra profile.
       Profile     profile_idc             profile-iop
                       (hexadecimal)           (binary)
           CB          42 (B)                  x1xx0000
             same as:  4D (M)                  1xxx0000
             same as:  58 (E)                  11xx0000
           B           42 (B)                  x0xx0000
             same as:  58 (E)                  10xx0000
           M           4D (M)                  0x0x0000
           E           58                      00xx0000
           H           64                      00000000
           H10         6E                      00000000
           H42         7A                      00000000
           H44         F4                      00000000
           H10I        6E                      00010000
           H42I        7A                      00010000
           H44I        F4                      00010000
           C44I        2C                      00010000
           SB          53                      x0000000
           SH          56                      0x000000
           SHI         56                      0x010000
       For example, in the table above, profile_idc equal to 58
       (Extended) with profile-iop equal to 11xx0000 indicates the
       same sub-profile corresponding to profile_idc equal to 42
       (Baseline) with profile-iop equal to x1xx0000.  Note that other
       combinations of profile_idc and profile-iop (not listed in
       Table 13) may represent a sub-profile equivalent to the common
       subset of coding tools for more than one profile.  Note also
       that a decoder conforming to a certain profile may be able to
       decode bitstreams conforming to other profiles.
       If profile-level-id is used to indicate stream properties, it
       indicates that, to decode the stream, the minimum subset of
       coding tools a decoder has to support is the default sub-
       profile, and the lowest level the decoder has to support is the
       default level.
       If the profile-level-id parameter is used for capability
       exchange or session setup, it indicates the subset of coding
       tools, which is equal to the default sub-profile, that the
       codec supports for both receiving and sending.  If max-recv-
       level is not present, the default level from profile-level-id
       indicates the highest level the codec wishes to support.  If

Wenger, et al. Standards Track [Page 62] RFC 6190 RTP Payload Format for SVC May 2011

       max-recv-level is present, it indicates the highest level the
       codec supports for receiving.  For either receiving or sending,
       all levels that are lower than the highest level supported MUST
       also be supported.
          Informative note: Capability exchange and session setup
          procedures should provide means to list the capabilities for
          each supported sub-profile separately.  For example, the
          one-of-N codec selection procedure of the SDP Offer/Answer
          model can be used (Section 10.2 of [RFC3264]).  The one-of-N
          codec selection procedure may also be used to provide
          different combinations of profile_idc and profile-iop that
          represent the same sub-profile.  When there are many
          different combinations of profile_idc and profile-iop that
          represent the same sub-profile, using the one-of-N codec
          selection procedure may result in a fairly large SDP
          message.  Therefore, a receiver should understand the
          different equivalent combinations of profile_idc and
          profile-iop that represent the same sub-profile, and be
          ready to accept an offer using any of the equivalent
          combinations.
       If no profile-level-id is present, the Baseline Profile without
       additional constraints at Level 1 MUST be implied.
    max-recv-level:
       This parameter MAY be used to indicate the highest level a
       receiver supports when the highest level is higher than the
       default level (the level indicated by profile-level-id).  The
       value of max-recv-level is a base16 (hexadecimal)
       representation of the two bytes after the syntax element
       profile_idc in the sequence parameter set NAL unit specified in
       [H.264]: profile-iop (as defined above) and level_idc.  If (the
       level_idc byte of max-recv-level is equal to 11 and bit 4 of
       the profile-iop byte of max-recv-level is equal to 1) or (the
       level_idc byte of max-recv-level is equal to 9 and bit 4 of the
       profile-iop byte of max-recv-level is equal to 0), the highest
       level the receiver supports is Level 1b.  Otherwise, the
       highest level the receiver supports is equal to the level_idc
       byte of max-recv-level divided by 10.
       max-recv-level MUST NOT be present if the highest level the
       receiver supports is not higher than the default level.
    max-recv-base-level:
       This parameter MAY be used to indicate the highest level a
       receiver supports for the base layer when negotiating an SVC
       stream.  The value of max-recv-base-level is a base16

Wenger, et al. Standards Track [Page 63] RFC 6190 RTP Payload Format for SVC May 2011

       (hexadecimal) representation of the two bytes after the syntax
       element profile_idc in the sequence parameter set NAL unit
       specified in [H.264]: profile-iop (as defined above) and
       level_idc.  If (the level_idc byte of max-recv-level is equal
       to 11 and bit 4 of the profile-iop byte of max-recv-level is
       equal to 1) or (the level_idc byte of max-recv-level is equal
       to 9 and bit 4 of the profile-iop byte of max-recv-level is
       equal to 0), the highest level the receiver supports for the
       base layer is Level 1b. Otherwise, the highest level the
       receiver supports for the base layer is equal to the level_idc
       byte of max-recv-level divided by 10.
    max-mbps, max-fs, max-cpb, max-dpb, and max-br:
       The common properties of these parameters are specified in
       [RFC6184].
    max-mbps: This parameter is as specified in [RFC6184].
    max-fs: This parameter is as specified in [RFC6184].
    max-cpb: The value of max-cpb is an integer indicating the maximum
       coded picture buffer size in units of 1000 bits for the VCL HRD
       parameters and in units of 1200 bits for the NAL HRD
       parameters.  Note that this parameter does not use units of
       cpbBrVclFactor and cpbBrNALFactor (see Table A-1 of [H.264]).
       The max-cpb parameter signals that the receiver has more memory
       than the minimum amount of coded picture buffer memory required
       by the signaled highest level conveyed in the value of the
       profile-level-id parameter or the max-recv-level parameter.
       When max-cpb is signaled, the receiver MUST be able to decode
       NAL unit streams that conform to the signaled highest level,
       with the exception that the MaxCPB value in Table A-1 of
       [H.264] for the signaled highest level is replaced with the
       value of max-cpb (after taking cpbBrVclFactor and
       cpbBrNALFactor into consideration when needed).  The value of
       max-cpb (after taking cpbBrVclFactor and cpbBrNALFactor into
       consideration when needed) MUST be greater than or equal to the
       value of MaxCPB given in Table A-1 of [H.264] for the highest
       level.  Senders MAY use this knowledge to construct coded video
       streams with greater variation of bitrate than can be achieved
       with the MaxCPB value in Table A-1 of [H.264].

Wenger, et al. Standards Track [Page 64] RFC 6190 RTP Payload Format for SVC May 2011

          Informative note: The coded picture buffer is used in the
          Hypothetical Reference Decoder (HRD, Annex C) of [H.264].
          The use of the HRD is recommended in SVC encoders to verify
          that the produced bitstream conforms to the standard and to
          control the output bitrate.  Thus, the coded picture buffer
          is conceptually independent of any other potential buffers
          in the receiver, including de-interleaving, re-multiplexing,
          and de-jitter buffers.  The coded picture buffer need not be
          implemented in decoders as specified in Annex C of [H.264];
          standard-compliant decoders can have any buffering
          arrangements provided that they can decode standard-
          compliant bitstreams.  Thus, in practice, the input buffer
          for video decoder can be integrated with the de-
          interleaving, re-multiplexing, and de-jitter buffers of the
          receiver.
    max-dpb: This parameter is as specified in [RFC6184].
    max-br: The value of max-br is an integer indicating the maximum
       video bitrate in units of 1000 bits per second for the VCL HRD
       parameters and in units of 1200 bits per second for the NAL HRD
       parameters.  Note that this parameter does not use units of
       cpbBrVclFactor and cpbBrNALFactor (see Table A-1 of [H.264]).
       The max-br parameter signals that the video decoder of the
       receiver is capable of decoding video at a higher bitrate than
       is required by the signaled highest level conveyed in the value
       of the profile-level-id parameter or the max-recv-level
       parameter.
       When max-br is signaled, the video codec of the receiver MUST
       be able to decode NAL unit streams that conform to the signaled
       highest level, with the following exceptions in the limits
       specified by the highest level:
       o  The value of max-br (after taking cpbBrVclFactor and
          cpbBrNALFactor into consideration when needed) replaces the
          MaxBR value in Table A-1 of [H.264] for the highest level.
       o  When the max-cpb parameter is not present, the result of the
          following formula replaces the value of MaxCPB in Table A-1
          of [H.264]: (MaxCPB of the signaled level) * max-br / (MaxBR
          of the signaled highest level).
       For example, if a receiver signals capability for Main profile
       Level 1.2 with max-br equal to 1550, this indicates a maximum
       video bitrate of 1550 kbits/sec for VCL HRD parameters, a

Wenger, et al. Standards Track [Page 65] RFC 6190 RTP Payload Format for SVC May 2011

       maximum video bitrate of 1860 kbits/sec for NAL HRD parameters,
       and a CPB size of 4036458 bits (1550000 / 384000 * 1000 *
       1000).
       The value of max-br (after taking cpbBrVclFactor and
       cpbBrNALFactor into consideration when needed) MUST be greater
       than or equal to the value MaxBR given in Table A-1 of [H.264]
       for the signaled highest level.
       Senders MAY use this knowledge to send higher-bitrate video as
       allowed in the level definition of SVC, to achieve improved
       video quality.
          Informative note: This parameter was added primarily to
          complement a similar codepoint in the ITU-T Recommendation
          H.245, so as to facilitate signaling gateway designs.  No
          assumption can be made from the value of this parameter that
          the network is capable of handling such bitrates at any
          given time.  In particular, no conclusion can be drawn that
          the signaled bitrate is possible under congestion control
          constraints.
    redundant-pic-cap:
       This parameter is as specified in [RFC6184].
    sprop-parameter-sets:
       This parameter MAY be used to convey any sequence parameter
       set, subset sequence parameter set, and picture parameter set
       NAL units (herein referred to as the initial parameter set NAL
       units) that can be placed in the NAL unit stream to precede any
       other NAL units in decoding order and that are associated with
       the default level of profile-level-id.  The parameter MUST NOT
       be used to indicate codec capability in any capability exchange
       procedure.  The value of the parameter is a comma (',')
       separated list of base64 [RFC4648] representations of the
       parameter set NAL units as specified in Sections 7.3.2.1,
       7.3.2.2, and G.7.3.2.1 of [H.264].  Note that the number of
       bytes in a parameter set NAL unit is typically less than 10,
       but a picture parameter set NAL unit can contain several
       hundreds of bytes.
          Informative note: When several payload types are offered in
          the SDP Offer/Answer model, each with its own sprop-
          parameter-sets parameter, then the receiver cannot assume
          that those parameter sets do not use conflicting storage
          locations (i.e., identical values of parameter set

Wenger, et al. Standards Track [Page 66] RFC 6190 RTP Payload Format for SVC May 2011

          identifiers).  Therefore, a receiver should buffer all
          sprop-parameter-sets and make them available to the decoder
          instance that decodes a certain payload type.
    sprop-level-parameter-sets:
       This parameter MAY be used to convey any sequence, subset
       sequence, and picture parameter set NAL units (herein referred
       to as the initial parameter set NAL units) that can be placed
       in the NAL unit stream to precede any other NAL units in
       decoding order and that are associated with one or more levels
       different than the default level of profile-level-id.  The
       parameter MUST NOT be used to indicate codec capability in any
       capability exchange procedure.
       The sprop-level-parameter-sets parameter contains parameter
       sets for one or more levels that are different than the default
       level.  All parameter sets targeted for use when one level of
       the default sub-profile is accepted by a receiver are clustered
       and prefixed with a three-byte field that has the same syntax
       as profile-level-id.  This enables the receiver to install the
       parameter sets for the accepted level and discard the rest.
       The three-byte field is named PLId, and all parameter sets
       associated with one level are named PSL, which has the same
       syntax as sprop-parameter-sets.  Parameter sets for each level
       are represented in the form of PLId:PSL, i.e., PLId followed by
       a colon (':') and the base64 [RFC4648] representation of the
       initial parameter set NAL units for the level.  Each pair of
       PLId:PSL is also separated by a colon.  Note that a PSL can
       contain multiple parameter sets for that level, separated with
       commas (',').
       The subset of coding tools indicated by each PLId field MUST be
       equal to the default sub-profile, and the level indicated by
       each PLId field MUST be different than the default level.
          Informative note: This parameter allows for efficient level
          downgrade or upgrade in SDP Offer/Answer and out-of-band
          transport of parameter sets, simultaneously.
    in-band-parameter-sets:
       This parameter MAY be used to indicate a receiver capability.
       The value MAY be equal to either 0 or 1.  The value 1 indicates
       that the receiver discards out-of-band parameter sets in sprop-
       parameter-sets and sprop-level-parameter-sets, therefore the
       sender MUST transmit all parameter sets in-band.  The value 0
       indicates that the receiver utilizes out-of-band parameter sets
       included in sprop-parameter-sets and/or sprop-level-parameter-
       sets.  However, in this case, the sender MAY still choose to

Wenger, et al. Standards Track [Page 67] RFC 6190 RTP Payload Format for SVC May 2011

       send parameter sets in-band.  When the parameter is not
       present, this receiver capability is not specified, and
       therefore the sender MAY send out-of-band parameter sets only,
       or it MAY send in-band-parameter-sets only, or it MAY send
       both.
    packetization-mode:
       This parameter is as specified in [RFC6184].  When the mst-mode
       parameter is present, the value of this parameter is
       additionally constrained as follows.  If mst-mode is equal to
       "NI-T", "NI-C", or "NI-TC", packetization-mode MUST NOT be
       equal to 2.  Otherwise, (mst-mode is equal to "I-C"),
       packetization-mode MUST be equal to 2.
    sprop-interleaving-depth:
       This parameter is as specified in [RFC6184].
    sprop-deint-buf-req:
       This parameter is as specified in [RFC6184].
    deint-buf-cap:
       This parameter is as specified in [RFC6184].
    sprop-init-buf-time:
       This parameter is as specified in [RFC6184].
    sprop-max-don-diff:
       This parameter is as specified in [RFC6184].
    max-rcmd-nalu-size:
       This parameter is as specified in [RFC6184].
    mst-mode:
       This parameter MAY be used to signal the properties of a NAL
       unit stream or the capabilities of a receiver implementation.
       If this parameter is present, multi-session transmission MUST
       be used.  Otherwise (this parameter is not present), single-
       session transmission MUST be used.  When this parameter is
       present, the following applies.  When the value of mst-mode is
       equal to "NI-T", the NI-T mode MUST be used.  When the value of
       mst-mode is equal to "NI-C", the NI-C mode MUST be used.  When
       the value of mst-mode is equal to "NI-TC", the NI-TC mode MUST
       be used.  When the value of mst-mode is equal to "I-C", the I-C
       mode MUST be used.  The value of mst-mode MUST have one of the
       following tokens: "NI-T", "NI-C", "NI-TC", or "I-C".
       All RTP sessions in an MST MUST have the same value of mst-
       mode.

Wenger, et al. Standards Track [Page 68] RFC 6190 RTP Payload Format for SVC May 2011

    sprop-mst-csdon-always-present:
       This parameter MUST NOT be present when mst-mode is not present
       or the value of mst-mode is equal to "NI-T" or "I-C".  This
       parameter signals the properties of the NAL unit stream.  When
       sprop-mst-csdon-always-present is present and the value is
       equal to 1, packetization-mode MUST be equal to 1, and all the
       RTP packets carrying the NAL unit stream MUST be STAP-A packets
       containing a PACSI NAL unit that further contains the DONC
       field or NI-MTAP packets with the J field equal to 1.  When
       sprop-mst-csdon-always-present is present and the value is
       equal to 1, the CS-DON value of any particular NAL unit can be
       derived solely according to information in the packet
       containing the NAL unit.
       When sprop-mst-csdon-always-present is present in the current
       RTP session, it MUST be present also in all the RTP sessions
       the current RTP session depends on and the value of sprop-mst-
       csdon-always-present is identical for the current RTP session
       and all the RTP sessions on which the current RTP session
       depends.
    sprop-mst-remux-buf-size:
       This parameter MUST NOT be present when mst-mode is not present
       or the value of mst-mode is equal to "NI-T".  This parameter
       MUST be present when mst-mode is present and the value of mst-
       mode is equal to "NI-C", "NI-TC", or "I-C".
       This parameter signals the properties of the NAL unit stream.
       It MUST be set to a value one less than the minimum re-
       multiplexing buffer size (in NAL units), so that it is
       guaranteed that receivers can reconstruct NAL unit decoding
       order as specified in Subsection 6.2.2.
       The value of sprop-mst-remux-buf-size MUST be an integer in the
       range of 0 to 32767, inclusive.
    sprop-remux-buf-req:
       This parameter MUST NOT be present when mst-mode is not present
       or the value of mst-mode is equal to "NI-T".  It MUST be
       present when mst-mode is present and the value of mst-mode is
       equal to "NI-C", "NI-TC", or "I-C".
       sprop-remux-buf-req signals the required size of the re-
       multiplexing buffer for the NAL unit stream.  It is guaranteed
       that receivers can recover the decoding order of the received
       NAL units from the current RTP session and the RTP sessions the

Wenger, et al. Standards Track [Page 69] RFC 6190 RTP Payload Format for SVC May 2011

       current RTP session depends on as specified in Section 6.2.2,
       when the re-multiplexing buffer size is of at least the value
       of sprop-remux-buf-req in units of bytes.
       The value of sprop-remux-buf-req MUST be an integer in the
       range of 0 to 4294967295, inclusive.
    remux-buf-cap:
       This parameter MUST NOT be present when mst-mode is not present
       or the value of mst-mode is equal to "NI-T".  This parameter
       MAY be used to signal the capabilities of a receiver
       implementation and indicates the amount of re-multiplexing
       buffer space in units of bytes that the receiver has available
       for recovering the NAL unit decoding order as specified in
       Section 6.2.2.  A receiver is able to handle any NAL unit
       stream for which the value of the sprop-remux-buf-req parameter
       is smaller than or equal to this parameter.
       If the parameter is not present, then a value of 0 MUST be used
       for remux-buf-cap.  The value of remux-buf-cap MUST be an
       integer in the range of 0 to 4294967295, inclusive.
    sprop-remux-init-buf-time:
       This parameter MAY be used to signal the properties of the NAL
       unit stream.  The parameter MUST NOT be present if mst-mode is
       not present or the value of mst-mode is equal to "NI-T".
       The parameter signals the initial buffering time that a
       receiver MUST wait before starting to recover the NAL unit
       decoding order as specified in Section 6.2.2 of this memo.
       The parameter is coded as a non-negative base10 integer
       representation in clock ticks of a 90-kHz clock.  If the
       parameter is not present, then no initial buffering time value
       is defined.  Otherwise, the value of sprop-remux-init-buf-time
       MUST be an integer in the range of 0 to 4294967295, inclusive.
    sprop-mst-max-don-diff:
       This parameter MAY be used to signal the properties of the NAL
       unit stream.  It MUST NOT be used to signal transmitter or
       receiver or codec capabilities.  The parameter MUST NOT be
       present if mst-mode is not present or the value of mst-mode is
       equal to "NI-T".  sprop-mst-max-don-diff is an integer in the
       range of 0 to 32767, inclusive.  If sprop-mst-max-don-diff is
       not present, the value of the parameter is unspecified.  sprop-
       mst-max-don-diff is calculated same as sprop-max-don-diff as
       specified in [RFC6184], with decoding order number being
       replaced by cross-session decoding order number.

Wenger, et al. Standards Track [Page 70] RFC 6190 RTP Payload Format for SVC May 2011

    sprop-scalability-info:
       This parameter MAY be used to convey the NAL unit containing
       the scalability information SEI message as specified in Annex G
       of [H.264].  This parameter MAY be used to signal the contained
       layers of an SVC bitstream.  The parameter MUST NOT be used to
       indicate codec capability in any capability exchange procedure.
       The value of the parameter is the base64 [RFC4648]
       representation of the NAL unit containing the scalability
       information SEI message.  If present, the NAL unit MUST contain
       only one SEI message that is a scalability information SEI
       message.
       This parameter MAY be used in an offering or declarative SDP
       message to indicate what layers (operation points) can be
       provided.  A receiver MAY indicate its choice of one layer
       using the optional media type parameter scalable-layer-id.
    scalable-layer-id:
       This parameter MAY be used to signal a receiver's choice of the
       offers or declared operation points or layers using sprop-
       scalability-info or sprop-operation-point-info.  The value of
       scalable-layer-id is a base16 representation of the layer_id[ i
       ] syntax element in the scalability information SEI message as
       specified in Annex G of [H.264] or layer-ID contained in sprop-
       operation-point-info.
    sprop-operation-point-info:
       This parameter MAY be used to describe the operation points of
       an RTP session.  The value of this parameter consists of a
       comma-separated list of operation-point-description vectors.
       The values given by the operation-point-description vectors are
       the same as, or are derived from, the values that would be
       given for a scalable layer in the scalability information SEI
       message as specified in Annex G of [H.264], where the term
       scalable layer in the scalability information SEI message
       refers to all NAL units associated with the same values of
       temporal_id, dependency_id, and quality_id.  In this memo, such
       a set of NAL units is called an operation point.
       Each operation-point-description vector has ten elements,
       provided as a comma-separated list of values as defined below.
       The first value of the operation-point-description vector is
       preceded by a '<', and the last value of the operation-point-
       description vector is followed by a '>'.  If the sprop-
       operation-point-info is followed by exactly one operation-
       point-description vector, this describes the highest operation
       point contained in the RTP session.  If there are two or more

Wenger, et al. Standards Track [Page 71] RFC 6190 RTP Payload Format for SVC May 2011

       operation-point-description vectors, the first describes the
       lowest and the last describes the highest operation point
       contained in the RTP session.
       The values given by the operation-point-description vector are
       as follows, in the order listed:
  1. layer-ID: This value specifies the layer identifier of the

operation point, which is identical to the layer_id that

          would be indicated (for the same values of dependency_id,
          quality_id, and temporal_id) in the scalability information
          SEI message.  This field MAY be empty, indicating that the
          value is unspecified.  When there are multiple operation-
          point-description vectors with layer-ID, the values of
          layer-ID do not need to be consecutive.
  1. temporal-ID: This value specifies the temporal_id of the

operation point. This field MUST NOT be empty.

  1. dependency-ID: This values specifies the dependency_id of

the operation point. This field MUST NOT be empty.

  1. quality-ID: This values specifies the quality_id of the

operation point. This field MUST NOT be empty.

  1. profile-level-ID: This value specifies the profile-level-idc

of the operation point in the base16 format. The default

          sub-profile or default level indicated by the parameter
          profile-level-ID in the sprop-operation-point-info vector
          SHALL be equal to or lower than the default sub-profile or
          default level indicated by profile-level-id, which may be
          either present or the default value is taken.  This field
          MAY be empty, indicating that the value is unspecified.
  1. avg-framerate: This value specifies the average frame rate

of the operation point. This value is given as an integer

          in frames per 256 seconds.  The field MAY be empty,
          indicating that the value is unspecified.
  1. width: This value specifies the width dimension in pixels of

decoded frames for the operation point. This parameter is

          not directly given in the scalability information SEI
          message.  This field MAY be empty, indicating that the value
          is unspecified.

Wenger, et al. Standards Track [Page 72] RFC 6190 RTP Payload Format for SVC May 2011

  1. height: This value gives the height dimension in pixels of

decoded frames for the operation point. This parameter is

          not directly given in the scalability information SEI.  This
          field MAY be empty, indicating that the value is
          unspecified.
  1. avg-bitrate: This value specifies the average bitrate of the

operation point. This parameter is given as an integer in

          kbits per second over the entire stream.  Note that this
          parameter is provided in the scalability information SEI
          message in bits per second and calculated over a variable
          time window.  This field MAY be empty, indicating that the
          value is unspecified.
  1. max-bitrate: This value specifies the maximum bitrate of the

operation point. This parameter is given as an integer in

          kbits per second and describes the maximum bitrate per each
          one-second window.  Note that this parameter is provided in
          the scalability information SEI message in bits per second
          and is calculated over a variable time window.  This field
          MAY be empty, indicating that the value is unspecified.
          Similarly to sprop-scalability-info, this parameter MAY be
          used in an offering or declarative SDP message to indicate
          what layers (operation points) can be provided.  A receiver
          MAY indicate its choice of the highest layer it wants to
          send and/or receive using the optional media type parameter
          scalable-layer-id.
    sprop-no-NAL-reordering-required:
       This parameter MAY be used to signal the properties of the NAL
       unit stream.  This parameter MUST NOT be present when mst-mode
       is not present or the value of mst-mode is not equal to "NI-T".
       The presence of this parameter indicates that no reordering of
       non-VCL or VCL NAL units is required for the decoding order
       recovery process.
    sprop-avc-ready:
       This parameter MAY be used to indicate the properties of the
       NAL unit stream.  The presence of this parameter indicates that
       the RTP session, if used in SST, or used in MST combined with
       other RTP sessions also with this parameter present, can be
       processed by a [RFC6184] receiver.  This parameter MAY be used
       with RTP sessions with media subtype H264-SVC.
    Encoding considerations:
       This media type is framed and binary; see Section 4.8 of RFC
       4288 [RFC4288].

Wenger, et al. Standards Track [Page 73] RFC 6190 RTP Payload Format for SVC May 2011

    Security considerations:
       See Section 8 of RFC 6190.
    Published specification:
       Please refer to RFC 6190 and its Section 13.
    Additional information:
       none
    File extensions:     none
    Macintosh file type code: none
    Object identifier or OID: none
    Person & email address to contact for further information:
       Ye-Kui Wang, yekui.wang@huawei.com
    Intended usage:      COMMON
    Restrictions on usage:
       This media type depends on RTP framing, and hence is only
       defined for transfer via RTP [RFC3550].  Transport within other
       framing protocols is not defined at this time.
    Interoperability considerations:
       The media subtype name contains "SVC" to avoid potential
       conflict with RFC 3984 and its potential future replacement RTP
       payload format for H.264 non-SVC profiles.
    Applications that use this media type:
       Real-time video applications like video streaming, video
       telephony, and video conferencing.
    Author:
       Ye-Kui Wang, yekui.wang@huawei.com
    Change controller:
       IETF Audio/Video Transport working group delegated from the
       IESG.

Wenger, et al. Standards Track [Page 74] RFC 6190 RTP Payload Format for SVC May 2011

7.2. SDP Parameters

7.2.1. Mapping of Payload Type Parameters to SDP

 The media type video/H264-SVC string is mapped to fields in the
 Session Description Protocol (SDP) as follows:
 o  The media name in the "m=" line of SDP MUST be video.
 o  The encoding name in the "a=rtpmap" line of SDP MUST be H264-SVC
    (the media subtype).
 o  The clock rate in the "a=rtpmap" line MUST be 90000.
 o  The OPTIONAL parameters profile-level-id, max-recv-level, max-
    recv-base-level, max-mbps, max-fs, max-cpb, max-dpb, max-br,
    redundant-pic-cap, in-band-parameter-sets, packetization-mode,
    sprop-interleaving-depth, deint-buf-cap, sprop-deint-buf-req,
    sprop-init-buf-time, sprop-max-don-diff, max-rcmd-nalu-size, mst-
    mode, sprop-mst-csdon-always-present, sprop-mst-remux-buf-size,
    sprop-remux-buf-req, remux-buf-cap, sprop-remux-init-buf-time,
    sprop-mst-max-don-diff, and scalable-layer-id, when present, MUST
    be included in the "a=fmtp" line of SDP.  These parameters are
    expressed as a media type string, in the form of a semicolon-
    separated list of parameter=value pairs.
 o  The OPTIONAL parameters sprop-parameter-sets, sprop-level-
    parameter-sets, sprop-scalability-info, sprop-operation-point-
    info, sprop-no-NAL-reordering-required, and sprop-avc-ready, when
    present, MUST be included in the "a=fmtp" line of SDP or conveyed
    using the "fmtp" source attribute as specified in Section 6.3 of
    [RFC5576].  For a particular media format (i.e., RTP payload
    type), a sprop-parameter-sets or sprop-level-parameter-sets MUST
    NOT be both included in the "a=fmtp" line of SDP and conveyed
    using the "fmtp" source attribute.  When included in the "a=fmtp"
    line of SDP, these parameters are expressed as a media type
    string, in the form of a semicolon-separated list of
    parameter=value pairs.  When conveyed using the "fmtp" source
    attribute, these parameters are only associated with the given
    source and payload type as parts of the "fmtp" source attribute.
          Informative note: Conveyance of sprop-parameter-sets and
          sprop-level-parameter-sets using the "fmtp" source attribute
          allows for out-of-band transport of parameter sets in
          topologies like Topo-Video-switch-MCU [RFC5117].

Wenger, et al. Standards Track [Page 75] RFC 6190 RTP Payload Format for SVC May 2011

7.2.2. Usage with the SDP Offer/Answer Model

 When an SVC stream (with media subtype H264-SVC) is offered over RTP
 using SDP in an Offer/Answer model [RFC3264] for negotiation for
 unicast usage, the following limitations and rules apply:
 o  The parameters identifying a media format configuration for SVC
    are profile-level-id, packetization-mode, and mst-mode.  These
    media configuration parameters (except for the level part of
    profile-level-id) MUST be used symmetrically when the answerer
    does not include scalable-layer-id in the answer; i.e., the
    answerer MUST either maintain all configuration parameters or
    remove the media format (payload type) completely, if one or more
    of the parameter values are not supported.  Note that the level
    part of profile-level-id includes level_idc, and, for indication
    of level 1b when profile_idc is equal to 66, 77, or 88, bit 4
    (constraint_set3_flag) of profile-iop.  The level part of profile-
    level-id is changeable.
       Informative note: The requirement for symmetric use does not
       apply for the level part of profile-level-id, and does not
       apply for the other stream properties and capability
       parameters.
       Informative note: In [H.264], all the levels except for Level
       1b are equal to the value of level_idc divided by 10.  Level 1b
       is a level higher than Level 1.0 but lower than Level 1.1, and
       is signaled in an ad hoc manner.  For the Baseline, Main, and
       Extended profiles (with profile_idc equal to 66, 77, and 88,
       respectively), Level 1b is indicated by level_idc equal to 11
       (i.e., the same as level 1.1) and constraint_set3_flag equal to
       1.  For other profiles, Level 1b is indicated by level_idc
       equal to 9 (but note that Level 1b for these profiles is still
       higher than Level 1, which has level_idc equal to 10, and lower
       than Level 1.1).  In SDP Offer/Answer, an answer may indicate a
       level equal to or lower than the level indicated in the offer.
       Due to the ad hoc indication of Level 1b, offerers and
       answerers must check the value of bit 4 (constraint_set3_flag)
       of the middle octet of the parameter profile-level-id, when
       profile_idc is equal to 66, 77, or 88 and level_idc is equal to
       11.
    To simplify handling and matching of these configurations, the
    same RTP payload type number used in the offer should also be used
    in the answer, as specified in [RFC3264].  The same RTP payload
    type number used in the offer MUST also be used in the answer when
    the answer includes scalable-layer-id.  When the answer does not
    include scalable-layer-id, the answer MUST NOT contain a payload

Wenger, et al. Standards Track [Page 76] RFC 6190 RTP Payload Format for SVC May 2011

    type number used in the offer unless the configuration is exactly
    the same as in the offer or the configuration in the answer only
    differs from that in the offer with a level lower than the default
    level offered.
       Informative note: When an offerer receives an answer that does
       not include scalable-layer-id it has to compare payload types
       not declared in the offer based on the media type (i.e.,
       video/H264-SVC) and the above media configuration parameters
       with any payload types it has already declared.  This will
       enable it to determine whether the configuration in question is
       new or if it is equivalent to configuration already offered,
       since a different payload type number may be used in the
       answer.
    Since an SVC stream may contain multiple operation points, a
    facility is provided so that an answerer can select a different
    operation point than the entire SVC stream.  Specifically,
    different operation points MAY be described using the sprop-
    scalability-info or sprop-operation-point-info parameters.  The
    first one carries the entire scalability information SEI message
    defined in Annex G of [H.264], whereas the second one may be
    derived, e.g., as a subset of this SEI message that only contains
    key information about an operation point.  Operation points, in
    both cases, are associated with a layer identifier.
    If such information (sprop-operation-point-info or sprop-
    scalability-info) is provided in an offer, an answerer MAY select
    from the various operation points offered in the sprop-
    scalability-information or sprop-operation-point-info parameters
    by including scalable-layer-id in the answer.  By this, the
    answerer indicates its selection of a particular operation point
    in the received and/or in the sent stream.  When such operation
    point selection takes place, i.e., the answerer includes scalable-
    layer-id in the answer, the media configuration parameters MUST
    NOT be present in the answer.  Rather, the media configuration
    that the answerer will use for receiving and/or sending is the one
    used for the selected operation point as indicated in the offer.
       Informative note: The ability to perform operation point
       selection enables a receiver to utilize the scalable nature of
       an SVC stream.
 o  The parameter max-recv-level, when present, declares the highest
    level supported for receiving.  In case max-recv-level is not
    present, the highest level supported for receiving is equal to the

Wenger, et al. Standards Track [Page 77] RFC 6190 RTP Payload Format for SVC May 2011

    default level indicated by the level part of profile-level-id.
    max-recv-level, when present, MUST be higher than the default
    level.
 o  The parameter max-recv-base-level, when present, declares the
    highest level of the base layer supported for receiving.  When
    max-recv-base-level is not present, the highest level supported
    for the base layer is not constrained separately from the SVC
    stream containing the base layer.  The endpoint at the other side
    MUST NOT send a scalable stream for which the base layer is of a
    level higher than max-recv-base-level.  Parameters declaring
    receiver capabilities above the default level (max-mbps, max-
    smbps, max-fs, max-cpb, max-dpb, max-br, and max-recv-level) do
    not apply to the base layer when max-recv-base-level is present.
 o  The parameters sprop-deint-buf-req, sprop-interleaving-depth,
    sprop-max-don-diff, sprop-init-buf-time, sprop-mst-csdon-always-
    present, sprop-remux-buf-req, sprop-mst-remux-buf-size, sprop-
    remux-init-buf-time, sprop-mst-max-don-diff, sprop-scalability-
    information, sprop-operation-point-info, sprop-no-NAL-reordering-
    required, and sprop-avc-ready describe the properties of the NAL
    unit stream that the offerer or answerer is sending for the media
    format configuration.  This differs from the normal usage of the
    Offer/Answer parameters: normally such parameters declare the
    properties of the stream that the offerer or the answerer is able
    to receive.  When dealing with SVC, the offerer assumes that the
    answerer will be able to receive media encoded using the
    configuration being offered.
       Informative note: The above parameters apply for any stream
       sent by the declaring entity with the same configuration; i.e.,
       they are dependent on their source.  Rather than being bound to
       the payload type, the values may have to be applied to another
       payload type when being sent, as they apply for the
       configuration.
 o  The capability parameters max-mbps, max-fs, max-cpb, max-dpb, max-
    br, redundant-pic-cap, and max-rcmd-nalu-size MAY be used to
    declare further capabilities of the offerer or answerer for
    receiving.  These parameters MUST NOT be present when the
    direction attribute is sendonly, and the parameters describe the
    limitations of what the offerer or answerer accepts for receiving
    streams.
 o  When mst-mode is not present and packetization-mode is equal to 2,
    the following applies.

Wenger, et al. Standards Track [Page 78] RFC 6190 RTP Payload Format for SVC May 2011

    o  An offerer has to include the size of the de-interleaving
       buffer, sprop-deint-buf-req, in the offer.  To enable the
       offerer and answerer to inform each other about their
       capabilities for de-interleaving buffering, both parties are
       RECOMMENDED to include deint-buf-cap.  It is also RECOMMENDED
       to consider offering multiple payload types with different
       buffering requirements when the capabilities of the receiver
       are unknown.
 o  When mst-mode is present and equal to "NI-C", "NI-TC", or "I-C",
    the following applies.
    o  An offerer has to include sprop-remux-buf-req in the offer.  To
       enable the offerer and answerer to inform each other about
       their capabilities for re-multiplexing buffering, both parties
       are RECOMMENDED to include remux-buf-cap.  It is also
       RECOMMENDED to consider offering multiple payload types with
       different buffering requirements when the capabilities of the
       receiver are unknown.
 o  The sprop-parameter-sets or sprop-level-parameter-sets parameter,
    when present (included in the "a=fmtp" line of SDP or conveyed
    using the "fmtp" source attribute as specified in Section 6.3 of
    [RFC5576]), is used for out-of-band transport of parameter sets.
    However, when out-of-band transport of parameter sets is used,
    parameter sets MAY still be additionally transported in-band.
    The answerer MAY use either out-of-band or in-band transport of
    parameter sets for the stream it is sending, regardless of whether
    out-of-band parameter sets transport has been used in the offerer-
    to-answerer direction.  Parameter sets included in an answer are
    independent of those parameter sets included in the offer, as they
    are used for decoding two different video streams, one from the
    answerer to the offerer, and the other in the opposite direction.
    The following rules apply to transport of parameter sets in the
    offerer-to-answerer direction.
    o  An offer MAY include either or both of sprop-parameter- sets
       and sprop-level-parameter-sets.  If neither sprop-parameter-
       sets nor sprop-level-parameter-sets is present in the offer,
       then only in-band transport of parameter sets is used.
    o  If the answer includes in-band-parameter-sets equal to 1, then
       the offerer MUST transmit parameter sets in-band.  Otherwise,
       the following applies.

Wenger, et al. Standards Track [Page 79] RFC 6190 RTP Payload Format for SVC May 2011

       o  If the level to use in the offerer-to-answerer direction is
          equal to the default level in the offer, the following
          applies.
             The answerer MUST be prepared to use the parameter sets
             included in sprop-parameter-sets, when present, for
             decoding the incoming NAL unit stream, and ignore sprop-
             level-parameter-sets, when present.
             When sprop-parameter-sets is not present in the offer,
             in-band transport of parameter sets MUST be used.
       o  Otherwise (the level to use in the offerer-to-answerer
          direction is not equal to the default level in the offer),
          the following applies.
             The answerer MUST be prepared to use the parameter sets
             that are included in sprop-level-parameter-sets for the
             accepted level (i.e., the default level in the answer,
             which is also the level to use in the offerer-to-answerer
             direction), when present, for decoding the incoming NAL
             unit stream, and ignore all other parameter sets included
             in sprop-level-parameter-sets and sprop-parameter-sets,
             when present.
             When no parameter sets for the accepted level are present
             in the sprop-level-parameter-sets, in-band transport of
             parameter sets MUST be used.
    The following rules apply to transport of parameter sets in the
    answerer-to-offerer direction.
    o  An answer MAY include either sprop-parameter-sets or sprop-
       level-parameter-sets, but MUST NOT include both of the two.  If
       neither sprop-parameter-sets nor sprop-level-parameter-sets is
       present in the answer, then only in-band transport of parameter
       sets is used.
    o  If the offer includes in-band-parameter-sets equal to 1, then
       the answerer MUST NOT include sprop-parameter-sets or sprop-
       level-parameter-sets in the answer and MUST transmit parameter
       sets in-band.  Otherwise, the following applies.
       o  If the level to use in the answerer-to-offerer direction is
          equal to the default level in the answer, the following
          applies.

Wenger, et al. Standards Track [Page 80] RFC 6190 RTP Payload Format for SVC May 2011

             The offerer MUST be prepared to use the parameter sets
             included in sprop-parameter-sets, when present, for
             decoding the incoming NAL unit stream, and ignore sprop-
             level-parameter-sets, when present.
             When sprop-parameter-sets is not present in the answer,
             the answerer MUST transmit parameter sets in-band.
       o  Otherwise (the level to use in the answerer-to-offerer
          direction is not equal to the default level in the answer),
          the following applies.
             The offerer MUST be prepared to use the parameter sets
             that are included in sprop-level-parameter-sets for the
             level to use in the answerer-to-offerer direction, when
             present in the answer, for decoding the incoming NAL unit
             stream, and ignore all other parameter sets included in
             sprop-level-parameter-sets and sprop-parameter-sets, when
             present in the answer.
             When no parameter sets for the level to use in the
             answerer-to-offerer direction are present in sprop-level-
             parameter-sets in the answer, the answerer MUST transmit
             parameter sets in-band.
    When sprop-parameter-sets or sprop-level-parameter-sets is
    conveyed using the "fmtp" source attribute as specified in Section
    6.3 of [RFC5576], the receiver of the parameters MUST store the
    parameter sets included in the sprop-parameter-sets or sprop-
    level-parameter-sets for the accepted level and associate them to
    the source given as a part of the "fmtp" source attribute.
    Parameter sets associated with one source MUST only be used to
    decode NAL units conveyed in RTP packets from the same source.
    When this mechanism is in use, SSRC collision detection and
    resolution MUST be performed as specified in [RFC5576].
       Informative note: Conveyance of sprop-parameter-sets and sprop-
       level-parameter-sets using the "fmtp" source attribute may be
       used in topologies like Topo-Video-switch-MCU [RFC5117] to
       enable out-of-band transport of parameter sets.
 For streams being delivered over multicast, the following rules
 apply:
 o  The media format configuration is identified by profile-level- id,
    including the level part, packetization-mode, and mst-mode.  These
    media format configuration parameters (including the level part of
    profile-level-id) MUST be used symmetrically; i.e., the answerer

Wenger, et al. Standards Track [Page 81] RFC 6190 RTP Payload Format for SVC May 2011

    MUST either maintain all configuration parameters or remove the
    media format (payload type) completely.  Note that this implies
    that the level part of profile-level-id for Offer/Answer in
    multicast is not changeable.
    To simplify handling and matching of these configurations, the
    same RTP payload type number used in the offer should also be used
    in the answer, as specified in [RFC3264].  An answer MUST NOT
    contain a payload type number used in the offer unless the
    configuration is the same as in the offer.
 o  Parameter sets received MUST be associated with the originating
    source, and MUST be only used in decoding the incoming NAL unit
    stream from the same source.
 o  The rules for other parameters are the same as above for unicast
    as long as the above rules are obeyed.
 Table 14 lists the interpretation of all the parameters that MUST be
 used for the various combinations of offer, answer, and direction
 attributes.  Note that the two columns wherein the scalable-layer-id
 parameter is used only apply to answers, whereas the other columns
 apply to both offers and answers.
 Table 14.  Interpretation of parameters for various combinations of
 offers, answers, direction attributes, with and without scalable-
 layer-id.  Columns that do not indicate offer or answer apply to
 both.

Wenger, et al. Standards Track [Page 82] RFC 6190 RTP Payload Format for SVC May 2011

                                     sendonly --+
        answer: recvonly,scalable-layer-id --+  |
         recvonly w/o scalable-layer-id --+  |  |
 answer: sendrecv, scalable-layer-id --+  |  |  |
   sendrecv w/o scalable-layer-id --+  |  |  |  |
                                    |  |  |  |  |
 profile-level-id                   C  X  C  X  P
 max-recv-level                     R  R  R  R  -
 max-recv-base-level                R  R  R  R  -
 packetization-mode                 C  X  C  X  P
 mst-mode                           C  X  C  X  P
 sprop-avc-ready                    P  P  -  -  P
 sprop-deint-buf-req                P  P  -  -  P
 sprop-init-buf-time                P  P  -  -  P
 sprop-interleaving-depth           P  P  -  -  P
 sprop-max-don-diff                 P  P  -  -  P
 sprop-mst-csdon-always-present     P  P  -  -  P
 sprop-mst-max-don-diff             P  P  -  -  P
 sprop-mst-remux-buf-size           P  P  -  -  P
 sprop-no-NAL-reordering-required   P  P  -  -  P
 sprop-operation-point-info         P  P  -  -  P
 sprop-remux-buf-req                P  P  -  -  P
 sprop-remux-init-buf-time          P  P  -  -  P
 sprop-scalability-info             P  P  -  -  P
 deint-buf-cap                      R  R  R  R  -
 max-br                             R  R  R  R  -
 max-cpb                            R  R  R  R  -
 max-dpb                            R  R  R  R  -
 max-fs                             R  R  R  R  -
 max-mbps                           R  R  R  R  -
 max-rcmd-nalu-size                 R  R  R  R  -
 redundant-pic-cap                  R  R  R  R  -
 remux-buf-cap                      R  R  R  R  -
 in-band-parameter-sets             R  R  R  R  -
 sprop-parameter-sets               S  S  -  -  S
 sprop-level-parameter-sets         S  S  -  -  S
 scalable-layer-id                  X  O  X  O  -
 Legend:
 C: configuration for sending and receiving streams
 P: properties of the stream to be sent
 R: receiver capabilities
 S: out-of-band parameter sets
 O: operation point selection
 X: MUST NOT be present
 -: not usable, when present SHOULD be ignored

Wenger, et al. Standards Track [Page 83] RFC 6190 RTP Payload Format for SVC May 2011

 Parameters used for declaring receiver capabilities are in general
 downgradable; i.e., they express the upper limit for a sender's
 possible behavior.  Thus, a sender MAY select to set its encoder
 using only lower/lesser or equal values of these parameters.
 Parameters declaring a configuration point are not changeable, with
 the exception of the level part of the profile-level-id parameter for
 unicast usage.  This expresses values a receiver expects to be used
 and must be used verbatim on the sender side.  If level downgrading
 (for profile-level-id) is used, an answerer MUST NOT include the
 scalable-layer-id parameter.
 When a sender's capabilities are declared, and non-downgradable
 parameters are used in this declaration, then these parameters
 express a configuration that is acceptable for the sender to receive
 streams.  In order to achieve high interoperability levels, it is
 often advisable to offer multiple alternative configurations, e.g.,
 for the packetization mode.  It is impossible to offer multiple
 configurations in a single payload type.  Thus, when multiple
 configuration offers are made, each offer requires its own RTP
 payload type associated with the offer.
 A receiver SHOULD understand all media type parameters, even if it
 only supports a subset of the payload format's functionality.  This
 ensures that a receiver is capable of understanding when an offer to
 receive media can be downgraded to what is supported by the receiver
 of the offer.
 An answerer MAY extend the offer with additional media format
 configurations.  However, to enable their usage, in most cases a
 second offer is required from the offerer to provide the stream
 property parameters that the media sender will use.  This also has
 the effect that the offerer has to be able to receive this media
 format configuration, not only to send it.
 If an offerer wishes to have non-symmetric capabilities between
 sending and receiving, the offerer can allow asymmetric levels via
 level-asymmetry-allowed equal to 1.  Alternatively, the offerer can
 offer different RTP sessions, i.e., different media lines declared as
 "recvonly" and "sendonly", respectively.  This may have further
 implications on the system, and may require additional external
 semantics to associate the two media lines.

7.2.3. Dependency Signaling in Multi-Session Transmission

 If MST is used, the rules on signaling media decoding dependency in
 SDP as defined in [RFC5583] apply.  The rules on "hierarchical or
 layered encoding" with multicast in Section 5.7 of [RFC4566] do not

Wenger, et al. Standards Track [Page 84] RFC 6190 RTP Payload Format for SVC May 2011

 apply, i.e., the notation for Connection Data "c=" SHALL NOT be used
 with more than one address.  Additionally, the order of dependencies
 of the RTP sessions indicated by the "a=depend" attribute as defined
 in [RFC5583] MUST represent the decoding order of the VC) NAL units
 in an access unit, i.e., the order of session dependency is given
 from the base or the lowest enhancement RTP session (the most
 important) to the highest enhancement RTP session (the least
 important).

7.2.4. Usage in Declarative Session Descriptions

 When SVC over RTP is offered with SDP in a declarative style, as in
 Real Time Streaming Protocol (RTSP) [RFC2326] or Session Announcement
 Protocol (SAP) [RFC2974], the following considerations are necessary.
 o  All parameters capable of indicating both stream properties and
    receiver capabilities are used to indicate only stream properties.
    For example, in this case, the parameter profile-level-id declares
    the values used by the stream, not the capabilities for receiving
    streams.  This results in that the following interpretation of the
    parameters MUST be used:
    Declaring actual configuration or stream properties:
  1. profile-level-id
  2. packetization-mode
  3. mst-mode
  4. sprop-deint-buf-req
  5. sprop-interleaving-depth
  6. sprop-max-don-diff
  7. sprop-init-buf-time
  8. sprop-mst-csdon-always-present
  9. sprop-mst-remux-buf-size
  10. sprop-remux-buf-req
  11. sprop-remux-init-buf-time
  12. sprop-mst-max-don-diff
  13. sprop-scalability-info
  14. sprop-operation-point-info
  15. sprop-no-NAL-reordering-required
  16. sprop-avc-ready
    Out-of-band transporting of parameter sets:
  1. sprop-parameter-sets
  2. sprop-level-parameter-sets

Wenger, et al. Standards Track [Page 85] RFC 6190 RTP Payload Format for SVC May 2011

    Not usable (when present, they SHOULD be ignored):
  1. max-mbps
  2. max-fs
  3. max-cpb
  4. max-dpb
  5. max-br
  6. max-recv-level
  7. max-recv-base-level
  8. redundant-pic-cap
  9. max-rcmd-nalu-size
  10. deint-buf-cap
  11. remux-buf-cap
  12. scalable-layer-id
 o  A receiver of the SDP is required to support all parameters and
    values of the parameters provided; otherwise, the receiver MUST
    reject (RTSP) or not participate in (SAP) the session.  It falls
    on the creator of the session to use values that are expected to
    be supported by the receiving application.

7.3. Examples

 In the following examples, "{data}" is used to indicate a data string
 encoded as base64.

7.3.1. Example for Offering a Single SVC Session

 Example 1: The offerer offers one video media description including
 two RTP payload types.  The first payload type offers H264, and the
 second offers H264-SVC.  Both payload types have different fmtp
 parameters as profile-level-id, packetization-mode, and sprop-
 parameter-sets.
    Offerer -> Answerer SDP message:
    m=video 20000 RTP/AVP 97 96
    a=rtpmap:96 H264/90000
    a=fmtp:96 profile-level-id=4de00a; packetization-mode=0;
     sprop-parameter-sets={sps0},{pps0};
    a=rtpmap:97 H264-SVC/90000
    a=fmtp:97 profile-level-id=53000c; packetization-mode=1;
     sprop-parameter-sets={sps0},{pps0},{sps1},{pps1};
 If the answerer does not support media subtype H264-SVC, it can issue
 an answer accepting only the base layer offer (payload type 96).  In
 the following example, the receiver supports H264-SVC, so it lists
 payload type 97 first as the preferred option.

Wenger, et al. Standards Track [Page 86] RFC 6190 RTP Payload Format for SVC May 2011

    Answerer -> Offerer SDP message:
    m=video 40000 RTP/AVP 97 96
    a=rtpmap:96 H264/90000
    a=fmtp:96 profile-level-id=4de00a; packetization-mode=0;
     sprop-parameter-sets={sps2},{pps2};
    a=rtpmap:97 H264-SVC/90000
    a=fmtp:97 profile-level-id=53000c; packetization-mode=1;
     sprop-parameter-sets={sps2},{pps2},{sps3},{pps3};

7.3.2. Example for Offering a Single SVC Session Using

      scalable-layer-id
 Example 2: Offerer offers the same media configurations as shown in
 the example above for receiving and sending the stream, but using a
 single RTP payload type and including sprop-operation-point-info.
    Offerer -> Answerer SDP message:
    m=video 20000 RTP/AVP 97
    a=rtpmap:97 H264-SVC/90000
    a=fmtp:97 profile-level-id=53000c; packetization-mode=1;
     sprop-parameter-sets={sps0},{sps1},{pps0},{pps1};
     sprop-operation-point-info=<1,0,0,0,4de00a,3200,176,144,128,
    256>,<2,1,1,0,53000c,6400,352,288,256,512>;
 In this example, the receiver supports H264-SVC and chooses the lower
 operation point offered in the RTP payload type for sending and
 receiving the stream.
    Answerer -> Offerer SDP message:
    m=video 40000 RTP/AVP 97
    a=rtpmap:97 H264-SVC/90000
    a=fmtp:97 sprop-parameter-sets={sps2},{sps3},{pps2},{pps3};
     scalable-layer-id=1;
 In an equivalent example showing the use of sprop-scalability-info
 instead using the sprop-operation-point-info, the sprop-operation-
 point-info would be exchanged by the sprop-scalability-info followed
 by the binary (base16) representation of the Scalability Information
 SEI message.

7.3.3. Example for Offering Multiple Sessions in MST

 Example 3: In this example, the offerer offers a multi-session
 transmission with up to three sessions.  The base session media
 description includes payload types that are backward compatible with

Wenger, et al. Standards Track [Page 87] RFC 6190 RTP Payload Format for SVC May 2011

 [RFC6184], and three different payload types are offered.  The other
 two media are using payload types with media subtype H264-SVC.  In
 each media description, different values of profile-level-id,
 packetization-mode, mst-mode, and sprop-parameter-sets are offered.
    Offerer -> Answerer SDP message:
    a=group:DDP L1 L2 L3
    m=video 20000 RTP/AVP 96 97 98
    a=rtpmap:96 H264/90000
    a=fmtp:96 profile-level-id=4de00a; packetization-mode=0;
     mst-mode=NI-T; sprop-parameter-sets={sps0},{pps0};
    a=rtpmap:97 H264/90000
    a=fmtp:97 profile-level-id=4de00a; packetization-mode=1;
     mst-mode=NI-TC; sprop-parameter-sets={sps0},{pps0};
    a=rtpmap:98 H264/90000
    a=fmtp:98 profile-level-id=4de00a; packetization-mode=2;
     mst-mode=I-C; init-buf-time=156320;
     sprop-parameter-sets={sps0},{pps0};
    a=mid:L1
    m=video 20002 RTP/AVP 99 100
    a=rtpmap:99 H264-SVC/90000
    a=fmtp:99 profile-level-id=53000c; packetization-mode=1;
     mst-mode=NI-T; sprop-parameter-sets={sps1},{pps1};
    a=rtpmap:100 H264-SVC/90000
    a=fmtp:100 profile-level-id=53000c; packetization-mode=2;
     mst-mode=I-C; sprop-parameter-sets={sps1},{pps1};
    a=mid:L2
    a=depend:99 lay L1:96,97; 100 lay L1:98
    m=video 20004 RTP/AVP 101
    a=rtpmap:101 H264-SVC/90000
    a=fmtp:101 profile-level-id=53001F; packetization-mode=1;
     mst-mode=NI-T; sprop-parameter-sets={sps2},{pps2};
    a=mid:L3
    a=depend:101 lay L1:96,97 L2:99
 It is assumed that in this example the answerer only supports the NI-
 T mode for multi-session transmission.  For this reason, it chooses
 the corresponding payload type (96) for the base RTP session.  For
 the two enhancement RTP sessions, the answerer also chooses the
 payload types that use the NI-T mode (99 and 101).

Wenger, et al. Standards Track [Page 88] RFC 6190 RTP Payload Format for SVC May 2011

    Answerer -> Offerer SDP message:
    a=group:DDP L1 L2 L3
    m=video 40000 RTP/AVP 96
    a=rtpmap:96 H264/90000
    a=fmtp:96 profile-level-id=4de00a; packetization-mode=0;
     mst-mode=NI-T; sprop-parameter-sets={sps3},{pps3};
    a=mid:L1
    m=video 40002 RTP/AVP 99
    a=rtpmap:99 H264-SVC/90000
    a=fmtp:99 profile-level-id=53000c; packetization-mode=1;
     mst-mode=NI-T; sprop-parameter-sets={sps4},{pps4};
    a=mid:L2
    a=depend:99 lay L1:96
    m=video 40004 RTP/AVP 101
    a=rtpmap:101 H264-SVC/90000
    a=fmtp:101 profile-level-id=53001F; packetization-mode=1;
     mst-mode=NI-T; sprop-parameter-sets={sps5},{pps5};
    a=mid:L3
    a=depend:101 lay L1:96 L2:99

7.3.4. Example for Offering Multiple Sessions in MST Including

      Operation with Answerer Using scalable-layer-id
 Example 4: In this example, the offerer offers a multi-session
 transmission of three layers with up to two sessions.  The base
 session media description has a payload type that is backward
 compatible with [RFC6184].  Note that no parameter sets are provided,
 in which case in-band transport must be used.  The other media
 description contains two enhancement layers and uses the media
 subtype H264-SVC.  It includes two operation point definitions.
    Offerer -> Answerer SDP message:
    a=group:DDP L1 L2
    m=video 20000 RTP/AVP 96
    a=rtpmap:96 H264/90000
    a=fmtp:96 profile-level-id=4de00a; packetization-mode=0;
     mst-mode=NI-T;
    a=mid:L1
    m=video 20002 RTP/AVP 97
    a=rtpmap:97 H264-SVC/90000
    a=fmtp:97 profile-level-id=53001F; packetization-mode=1;
     mst-mode=NI-TC; sprop-operation-point-info=<2,0,1,0,53000c,
    3200,352,288,384,512>,<3,1,2,0,53001F,6400,704,576,768,1024>;
    a=mid:L2
    a=depend:97 lay L1:96

Wenger, et al. Standards Track [Page 89] RFC 6190 RTP Payload Format for SVC May 2011

 It is assumed that the answerer wants to send and receive the base
 layer (payload type 96), but it only wants to send and receive the
 lower enhancement layer, i.e., the one with layer id equal to 2.  For
 this reason, the response will include the selection of the desired
 layer by setting scalable-layer-id equal to 2.  Note that the answer
 only includes the scalable-layer-id information.  The answer could
 include sprop-parameter-sets in the response.
    Answerer -> Offerer SDP message:
    a=group:DDP L1 L2
    m=video 40000 RTP/AVP 96
    a=rtpmap:96 H264/90000
    a=fmtp:96 profile-level-id=4de00a; packetization-mode=0;
     mst-mode=NI-T;
    a=mid:L1
    m=video 40002 RTP/AVP 97
    a=rtpmap:97 H264-SVC/90000
    a=fmtp:97 scalable-layer-id=2;
    a=mid:L2
    a=depend:97 lay L1:96

7.3.5. Example for Negotiating an SVC Stream with a Constrained Base

      Layer in SST
 Example 5: The offerer (Alice) offers one video description including
 two RTP payload types with differing levels and packetization modes.
    Offerer -> Answerer SDP message:
    m=video 20000 RTP/AVP 97 96
    a=rtpmap:96 H264-SVC/90000
    a=fmtp:96 profile-level-id=53001e; packetization-mode=0;
    a=rtpmap:97 H264-SVC/90000
    a=fmtp:97 profile-level-id=53001f; packetization-mode=1;
 The answerer (Bridge) chooses packetization mode 1, and indicates
 that it would receive an SVC stream with the base layer being
 constrained.
    Answerer -> Offerer SDP message:
    m=video 40000 RTP/AVP 97
    a=rtpmap:97 H264-SVC/90000
    a=fmtp:97 profile-level-id=53001f; packetization-mode=1;
      max-recv-base-level=000d

Wenger, et al. Standards Track [Page 90] RFC 6190 RTP Payload Format for SVC May 2011

 The answering endpoint must send an SVC stream at Level 3.1.  Since
 the offering endpoint did not declare max-recv-base-level, the base
 layer of the SVC stream the answering endpoint must send is not
 specifically constrained.  The offering endpoint (Alice) must send an
 SVC stream at Level 3.1, for which the base layer must be of a level
 not higher than Level 1.3.

7.4. Parameter Set Considerations

 Section 8.4 of [RFC6184] applies in this memo, with the following
 applies additionally for multi-session transmission (MST).
 In MST, regardless of out-of-band or in-band transport of parameter
 sets are in use, parameter sets required for decoding NAL units
 carried in one particular RTP session SHOULD be carried in the same
 session, MAY be carried in a session that the particular RTP session
 depends on, and MUST NOT be carried in a session that the particular
 RTP session does not depend on.

8. Security Considerations

 The security considerations of the RTP Payload Format for H.264 Video
 specification [RFC6184] apply.  Additionally, the following applies.
 Decoders MUST exercise caution with respect to the handling of
 reserved NAL unit types and reserved SEI messages, particularly if
 they contain active elements, and MUST restrict their domain of
 applicability to the presentation containing the stream.  The safest
 way is to simply discard these NAL units and SEI messages.
 When integrity protection is applied to a stream, care MUST be taken
 that the stream being transported may be scalable; hence a receiver
 may be able to access only part of the entire stream.
 End-to-end security with either authentication, integrity, or
 confidentiality protection will prevent a MANE from performing media-
 aware operations other than discarding complete packets.  And in the
 case of confidentiality protection it will even be prevented from
 performing discarding of packets in a media-aware way.  To allow any
 MANE to perform its operations, it will be required to be a trusted
 entity that is included in the security context establishment.  This
 applies both for the media path and for the RTCP path, if RTCP
 packets need to be rewritten.

Wenger, et al. Standards Track [Page 91] RFC 6190 RTP Payload Format for SVC May 2011

9. Congestion Control

 Within any given RTP session carrying payload according to this
 specification, the provisions of Section 10 of [RFC6184] apply.
 Reducing the session bitrate is possible by one or more of the
 following means:
 a) Within the highest layer identified by the DID field remove any
    NAL units with QID higher than a certain value.
 b) Remove all NAL units with TID higher than a certain value.
 c) Remove all NAL units associated with a DID higher than a certain
    value.
       Informative note: Removal of all coded slice NAL units
       associated with DIDs higher than a certain value in the entire
       stream is required in order to preserve conformance of the
       resulting SVC stream.
 d) Utilize the PRID field to indicate the relative importance of NAL
    units, and remove all NAL units associated with a PRID higher than
    a certain value.  Note that the use of the PRID is application-
    specific.
 e) Remove NAL units or entire packets according to application-
    specific rules.  The result will depend on the particular coding
    structure used as well as any additional application-specific
    functionality (e.g., concealment performed at the receiving
    decoder).  In general, this will result in the reception of a non-
    conforming bitstream and hence the decoder behavior is not
    specified by [H.264].  Significant artifacts may therefore appear
    in the decoded output if the particular decoder implementation
    does not take appropriate action in response to congestion
    control.
    Informative note: The discussion above is centered on NAL units
    rather than packets, primarily because that is the level where
    senders can meaningfully manipulate the scalable bitstream.  The
    mapping of NAL units to RTP packets is fairly flexible when using
    aggregation packets.  Depending on the nature of the congestion
    control algorithm, the "dimension" of congestion measurement
    (packet count or bitrate) and reaction to it (reducing packet
    count or bitrate or both) can be adjusted accordingly.
 All aforementioned means are available to the RTP sender, regardless
 of whether that sender is located in the sending endpoint or in a
 mixer-based MANE.

Wenger, et al. Standards Track [Page 92] RFC 6190 RTP Payload Format for SVC May 2011

 When a translator-based MANE is employed, then the MANE MAY
 manipulate the session only on the MANE's outgoing path, so that the
 sensed end-to-end congestion falls within the permissible envelope.
 As with all translators, in this case, the MANE needs to rewrite RTCP
 RRs to reflect the manipulations it has performed on the session.
    Informative note: Applications MAY also implement, in addition or
    separately, other congestion control mechanisms, e.g., as
    described in [RFC5775] and [Yan].

10. IANA Considerations

 A new media type, as specified in Section 7.1 of this memo, has been
 registered with IANA.

11. Informative Appendix: Application Examples

11.1. Introduction

 Scalable video coding is a concept that has been around since at
 least MPEG-2 [MPEG2], which goes back as early as 1993.
 Nevertheless, it has never gained wide acceptance, perhaps partly
 because applications didn't materialize in the form envisioned during
 standardization.
 ISO/IEC MPEG and ITU-T VCEG, respectively, performed a requirement
 analysis for the SVC project.  The MPEG and VCEG requirement
 documents are available in [JVT-N026] and [JVT-N027], respectively.
 The following introduces four main application scenarios that the
 authors consider relevant and that are implementable with this
 specification.

11.2. Layered Multicast

 This well-understood form of the use of layered coding [McCanne]
 implies that all layers are individually conveyed in their own RTP
 packet streams, each carried in its own RTP session using the IP
 (multicast) address and port number as the single demultiplexing
 point.  Receivers "tune" into the layers by subscribing to the IP
 multicast, normally by using IGMP [IGMP].  Depending on the
 application scenario, it is also possible to convey a number of
 layers in one RTP session, when finer operation points within the
 subset of layers are not needed.
 Layered multicast has the great advantage of simplicity and easy
 implementation.  However, it has also the great disadvantage of
 utilizing many different transport addresses.  While the authors

Wenger, et al. Standards Track [Page 93] RFC 6190 RTP Payload Format for SVC May 2011

 consider this not to be a major problem for a professionally
 maintained content server, receiving client endpoints need to open
 many ports to IP multicast addresses in their firewalls.  This is a
 practical problem from a firewall and network address translation
 (NAT) viewpoint.  Furthermore, even today IP multicast is not as
 widely deployed as many wish.
 The authors consider layered multicast an important application
 scenario for the following reasons.  First, it is well understood and
 the implementation constraints are well known.  Second, there may
 well be large-scale IP networks outside the immediate Internet
 context that may wish to employ layered multicast in the future.  One
 possible example could be a combination of content creation and core-
 network distribution for the various mobile TV services, e.g., those
 being developed by 3GPP (MBMS) [MBMS] and DVB (DVB-H) [DVB-H].

11.3. Streaming

 In this scenario, a streaming server has a repository of stored SVC
 coded layers for a given content.  At the time of streaming, and
 according to the capabilities, connectivity, and congestion situation
 of the client(s), the streaming server generates and serves a
 scalable stream.  Both unicast and multicast serving is possible.  At
 the same time, the streaming server may use the same repository of
 stored layers to compose different streams (with a different set of
 layers) intended for other audiences.
 As every endpoint receives only a single SVC RTP session, the number
 of firewall pinholes can be optimized to one.
 The main difference between this scenario and straightforward
 simulcasting lies in the architecture and the requirements of the
 streaming server, and is therefore out of the scope of IETF
 standardization.  However, compelling arguments can be made why such
 a streaming server design makes sense.  One possible argument is
 related to storage space and channel bandwidth.  Another is bandwidth
 adaptability without transcoding -- a considerable advantage in a
 congestion controlled network.  When the streaming server learns
 about congestion, it can reduce the sending bitrate by choosing fewer
 layers when composing the layered stream; see Section 9.  SVC is
 designed to gracefully support both bandwidth ramp-down and bandwidth
 ramp-up with a considerable dynamic range.  This payload format is
 designed to allow for bandwidth flexibility in the mentioned sense.
 While, in theory, a transcoding step could achieve a similar dynamic
 range, the computational demands are impractically high and video
 quality is typically lowered -- therefore, few (if any) streaming
 servers implement full transcoding.

Wenger, et al. Standards Track [Page 94] RFC 6190 RTP Payload Format for SVC May 2011

11.4. Videoconferencing (Unicast to MANE, Unicast to Endpoints)

 Videoconferencing has traditionally relied on Multipoint Control
 Units (MCUs).  These units connect endpoints in a star configuration
 and operate as follows.  Coded video is transmitted from each
 endpoint to the MCU, where it is decoded, scaled, and composited to
 construct output frames, which are then re-encoded and transmitted to
 the endpoint(s).  In systems supporting personalized layout (each
 user is allowed to select the layout of his/her screen), the
 compositing and encoding process is performed for each of the
 receiving endpoints.  Even without personalized layout, rate matching
 still requires that the encoding process at the MCU is performed
 separately for each endpoint.  As a result, MCUs have considerable
 complexity and introduce significant delay.  The cascaded encodings
 also reduce the video quality.  Particularly for multipoint
 connections, interactive communication is cumbersome as the end-to-
 end delay is very high [G.114].  A simpler architecture is the
 switching MCU, in which one of the incoming video streams is
 redirected to the receiving endpoints.  Obviously, only one user at a
 time can be seen and rate matching cannot be performed, thus forcing
 all transmitting endpoints to transmit at the lowest bit rate
 available in the MCU-to-endpoint connections.
 With scalable video coding the MCU can be replaced with an
 application-level router (ALR): this unit simply selects which
 incoming packets should be transmitted to which of the receiving
 endpoints [Eleft].  In such a system, each endpoint performs its own
 composition of the incoming video streams.  Assuming, for example, a
 system that uses spatial scalability with two layers, personalized
 layout is equivalent to instructing the ALR to only send the required
 packets for the corresponding resolution to the particular endpoint.
 Similarly, rate matching at the ALR for a particular endpoint can be
 performed by selecting an appropriate subset of the incoming video
 packets to transmit to the particular endpoint.  Personalized layout
 and rate matching thus become routing decisions, and require no
 signal processing.  Note that scalability also allows participants to
 enjoy the best video quality afforded by their links, i.e., users no
 longer have to be forced to operate at the quality supported by the
 weakest endpoint.  Most importantly, the ALR has an insignificant
 contribution to the end-to-end delay, typically an order of magnitude
 less than an MCU.  This makes it possible to have fully interactive
 multipoint conferences with even a very large number of participants.
 There are significant advantages as well in terms of error resilience
 and, in fact, error tolerance can be increased by nearly an order of
 magnitude here as well (e.g., using unequal error protection).
 Finally, the very low delay of an ALR allows these systems to be

Wenger, et al. Standards Track [Page 95] RFC 6190 RTP Payload Format for SVC May 2011

 cascaded, with significant benefits in terms of system design and
 deployment.  Cascading of traditional MCUs is impossible due to the
 very high delay that even a single MCU introduces.
 Scalable video coding enables a very significant paradigm shift in
 videoconferencing systems, bringing the complexity of video
 communication systems (particularly the servers residing within the
 network) in line with other types of network applications.

11.5. Mobile TV (Multicast to MANE, Unicast to Endpoint)

 This scenario is a bit more complex, and designed to optimize the
 network traffic in a core network, while still requiring only a
 single pinhole in the endpoint's firewall.  One of its key
 applications is the mobile TV market.
 Consider a large private IP network, e.g., the core network of the
 Third Generation Partnership Project (3GPP).  Streaming servers
 within this core network can be assumed to be professionally
 maintained.  It is assumed that these servers can have many ports
 open to the network and that layered multicast is a real option.
 Therefore, the streaming server multicasts SVC scalable layers,
 instead of simulcasting different representations of the same content
 at different bitrates.
 Also consider many endpoints of different classes.  Some of these
 endpoints may lack the processing power or the display size to
 meaningfully decode all layers; others may have these capabilities.
 Users of some endpoints may wish not to pay for high quality and are
 happy with a base service, which may be cheaper or even free.  Other
 users are willing to pay for high quality.  Finally, some connected
 users may have a bandwidth problem in that they can't receive the
 bandwidth they would want to receive -- be it through congestion,
 connectivity, change of service quality, or for whatever other
 reasons.  However, all these users have in common that they don't
 want to be exposed too much, and therefore the number of firewall
 pinholes needs to be small.
 This situation can be handled best by introducing middleboxes close
 to the edge of the core network, which receive the layered multicast
 streams and compose the single SVC scalable bitstream according to
 the needs of the endpoint connected.  These middleboxes are called
 MANEs throughout this specification.  In practice, the authors
 envision the MANE to be part of (or at least physically and
 topologically close to) the base station of a mobile network, where
 all the signaling and media traffic necessarily are multiplexed on
 the same physical link.

Wenger, et al. Standards Track [Page 96] RFC 6190 RTP Payload Format for SVC May 2011

 MANEs necessarily need to be fairly complex devices.  They certainly
 need to understand the signaling, so, for example, to associate the
 payload type octet in the RTP header with the SVC payload type.
 A MANE may aggregate multiple RTP streams, possibly from multiple RTP
 sessions, thus to reduce the number of firewall pinholes required at
 the endpoints, or may optimize the outgoing RTP stream to the MTU
 size of the outgoing path by utilizing the aggregation and
 fragmentation mechanisms of this memo.  This type of MANE is
 conceptually easy to implement and can offer powerful features,
 primarily because it necessarily can "see" the payload (including the
 RTP payload headers), utilize the wealth of layering information
 available therein, and manipulate it.
 A MANE can also perform stream thinning, in order to adhere to
 congestion control principles as discussed in Section 9.  While the
 implementation of the forward (media) channel of such a MANE appears
 to be comparatively simple, the need to rewrite RTCP RRs makes even
 such a MANE a complex device.
 While the implementation complexity of either case of a MANE, as
 discussed above, is fairly high, the computational demands are
 comparatively low.

12. Acknowledgements

 Miska Hannuksela contributed significantly to the designs of the
 PACSI NAL unit and the NI-C mode for decoding order recovery.  Roni
 Even organized and coordinated the design team for the development of
 this memo, and provided valuable comments.  Jonathan Lennox
 contributed to the NAL unit reordering algorithm for MST and provided
 input on several parts of this memo.  Peter Amon, Sam Ganesan, Mike
 Nilsson, Colin Perkins, and Thomas Wiegand were members of the design
 team and provided valuable contributions.  Magnus Westerlund has also
 made valuable comments.  Charles Eckel and Stuart Taylor provided
 valuable comments after the first WGLC for this document.  Xiaohui
 (Joanne) Wei helped improving Table 13 and the SDP examples.
 The work of Thomas Schierl has been supported by the European
 Commission under contract number FP7-ICT-248036, project COAST.

13. References

13.1. Normative References

 [H.264]    ITU-T Recommendation H.264, "Advanced video coding for
            generic audiovisual services", March 2010.

Wenger, et al. Standards Track [Page 97] RFC 6190 RTP Payload Format for SVC May 2011

 [RFC6184]  Wang, Y.-K., Even, R., Kristensen, T., and R. Jesup, "RTP
            Payload Format for H.264 Video", RFC 6184, May 2011.
 [ISO/IEC14496-10]
            ISO/IEC International Standard 14496-10:2005.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
            with Session Description Protocol (SDP)", RFC 3264, June
            2002.
 [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
            Jacobson, "RTP: A Transport Protocol for Real-Time
            Applications", STD 64, RFC 3550, July 2003.
 [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
            Registration Procedures", BCP 13, RFC 4288, December 2005.
 [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
            Description Protocol", RFC 4566, July 2006.
 [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
            Encodings", RFC 4648, October 2006.
 [RFC5576]  Lennox, J., Ott, J., and T. Schierl, "Source-Specific
            Media Attributes in the Session Description Protocol
            (SDP)", RFC 5576, June 2009.
 [RFC5583]  Schierl, T. and S. Wenger, "Signaling Media Decoding
            Dependency in the Session Description Protocol (SDP)", RFC
            5583, July 2009.
 [RFC6051]  Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP
            Flows", RFC 6051, November 2010.

13.2. Informative References

 [DVB-H]    DVB - Digital Video Broadcasting (DVB); DVB-H
            Implementation Guidelines, ETSI TR 102 377, 2005.
 [Eleft]    Eleftheriadis, A., R. Civanlar, and O. Shapiro,
            "Multipoint Videoconferencing with Scalable Video Coding",
            Journal of Zhejiang University SCIENCE A, Vol. 7, Nr. 5,
            April 2006, pp. 696-705. (Proceedings of the Packet Video
            2006 Workshop.)

Wenger, et al. Standards Track [Page 98] RFC 6190 RTP Payload Format for SVC May 2011

 [G.114]    ITU-T Rec. G.114, "One-way transmission time", May 2003.
 [H.241]    ITU-T Rec. H.241, "Extended video procedures and control
            signals for H.300-series terminals", May 2006.
 [IGMP]     Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
            Thyagarajan, "Internet Group Management Protocol, Version
            3", RFC 3376, October 2002.
 [JVT-N026] Ohm J.-R., Koenen, R., and Chiariglione, L. (ed.), "SVC
            requirements specified by MPEG (ISO/IEC JTC1 SC29 WG11)",
            JVT-N026, available from http://ftp3.itu.ch/av-arch/
            jvt-site/2005_01_HongKong/JVT-N026.doc, Hong Kong, China,
            January 2005.
 [JVT-N027] Sullivan, G. and Wiegand, T. (ed.), "SVC requirements
            specified by VCEG (ITU-T SG16 Q.6)", JVT-N027, available
            from http://ftp3.itu.int/av-arch/
            jvt-site/2005_01_HongKong/JVT-N027.doc, Hong Kong, China,
            January 2005.
 [McCanne]  McCanne, S., Jacobson, V., and Vetterli, M., "Receiver-
            driven layered multicast", in Proc. of ACM SIGCOMM'96,
            pages 117-130, Stanford, CA, August 1996.
 [MBMS]     3GPP - Technical Specification Group Services and System
            Aspects; Multimedia Broadcast/Multicast Service (MBMS);
            Protocols and codecs (Release 6), December 2005.
 [MPEG2]    ISO/IEC International Standard 13818-2:1993.
 [RFC2326]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
            Streaming Protocol (RTSP)", RFC 2326, April 1998.
 [RFC2974]  Handley, M., Perkins, C., and E. Whelan, "Session
            Announcement Protocol", RFC 2974, October 2000.
 [RFC5117]  Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117,
            January 2008.
 [RFC5775]  Luby, M., Watson, M., and L. Vicisano, "Asynchronous
            Layered Coding (ALC) Protocol Instantiation", RFC 5775,
            April 2010.
 [Yan]      Yan, J., Katrinis, K., May, M., and Plattner, R., "Media-
            and TCP-friendly congestion control for scalable video
            streams", in IEEE Trans. Multimedia, pages 196-206, April
            2006.

Wenger, et al. Standards Track [Page 99] RFC 6190 RTP Payload Format for SVC May 2011

Authors' Addresses

 Stephan Wenger
 2400 Skyfarm Dr.
 Hillsborough, CA 94010
 USA
 Phone: +1-415-713-5473
 EMail: stewe@stewe.org
 Ye-Kui Wang
 Huawei Technologies
 400 Crossing Blvd, 2nd Floor
 Bridgewater, NJ 08807
 USA
 Phone: +1-908-541-3518
 EMail: yekui.wang@huawei.com
 Thomas Schierl
 Fraunhofer HHI
 Einsteinufer 37
 D-10587 Berlin
 Germany
 Phone: +49-30-31002-227
 EMail: ts@thomas-schierl.de
 Alex Eleftheriadis
 Vidyo, Inc.
 433 Hackensack Ave.
 Hackensack, NJ 07601
 USA
 Phone: +1-201-467-5135
 EMail: alex@vidyo.com

Wenger, et al. Standards Track [Page 100]

/data/webs/external/dokuwiki/data/pages/rfc/rfc6190.txt · Last modified: 2011/05/07 00:13 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki