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rfc:rfc6185

Internet Engineering Task Force (IETF) T. Kristensen Request for Comments: 6185 P. Luthi Category: Standards Track TANDBERG ISSN: 2070-1721 May 2011

                       RTP Payload Format for
      H.264 Reduced-Complexity Decoding Operation (RCDO) Video

Abstract

 This document describes an RTP payload format for the Reduced-
 Complexity Decoding Operation (RCDO) for H.264 Baseline profile
 bitstreams, as specified in ITU-T Recommendation H.241.  RCDO reduces
 the decoding cost and resource consumption of the video processing.
 The RCDO RTP payload format is based on the H.264 RTP payload format.

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/rfc6185.

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.

Kristensen & Luthi Standards Track [Page 1] RFC 6185 H.264 RCDO RTP Payload May 2011

 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.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
 2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
 3.  Media Format Background  . . . . . . . . . . . . . . . . . . .  3
 4.  Payload Format . . . . . . . . . . . . . . . . . . . . . . . .  3
 5.  Congestion Control Considerations  . . . . . . . . . . . . . .  3
 6.  Payload Format Parameters  . . . . . . . . . . . . . . . . . .  3
   6.1.  Media Type Definition  . . . . . . . . . . . . . . . . . .  4
 7.  Mapping to SDP . . . . . . . . . . . . . . . . . . . . . . . . 19
   7.1.  Offer/Answer Considerations  . . . . . . . . . . . . . . . 20
   7.2.  Declarative SDP Considerations . . . . . . . . . . . . . . 20
 8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
 9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
   11.1. Normative References . . . . . . . . . . . . . . . . . . . 21
   11.2. Informative References . . . . . . . . . . . . . . . . . . 21

1. Introduction

 ITU-T Recommendation H.241 [3] specifies a Reduced-Complexity
 Decoding Operation (RCDO) for use with H.264 [2] Baseline profile
 bitstreams.  It also specifies a bitstream constraint associated with
 RCDO and a mechanism for signaling RCDO within the bitstream.  The
 RCDO signaling indicates that the bitstream conforms to the bitstream
 constraint and that the decoder shall apply the RCDO decoding process
 to the bitstream.
 RCDO for H.264 offers a solution to support higher resolutions at the
 same high frame rates used in current implementations.  This is
 achieved by reducing the processing requirements and thus reducing
 the decoding cost/resource consumption of the video processing.
 This document defines media type parameters and allows use in systems
 based on the Session Description Protocol (SDP) [8] for signaling.

Kristensen & Luthi Standards Track [Page 2] RFC 6185 H.264 RCDO RTP Payload May 2011

2. Conventions Used in This Document

 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 [4].

3. Media Format Background

 The Reduced-Complexity Decoding Operation (RCDO) for H.264 Baseline
 profile bitstreams is specified in Annex B of H.241 [3].  RCDO is
 specified as a separate H.264 mode and is distinct from any profile
 defined in H.264.  An RCDO bitstream obeys all the constraints of the
 Baseline profile.
 The media format is based on the H.264 RTP payload format as
 specified in RFC 6184 [1].  Therefore, RFC 6184 constitutes the basis
 for this document and is referred to several times.
 In order to signal H.264 additional modes, Table 8-13 of H.241 [3]
 specifies an AdditionalModesSupported parameter.  Currently, the only
 additional mode defined is RCDO.
    Informative note: Other additional modes may be defined in the
    future.  H.264 additional modes may or may not be distinct from
    the profiles in H.264.
 A separate media subtype, named H264-RCDO, is defined to ensure
 backward compatibility with deployed implementations of H.264.

4. Payload Format

 The payload format defined in Section 5 of RFC 6184 [1] SHALL be
 used.  This includes the RTP header usage and the payload format in
 RFC 6184.  Examples of typical RTP packets can be found in RFC 6184.

5. Congestion Control Considerations

 Congestion control for RTP SHALL be used in accordance with RFC 3550
 [6] and with any applicable RTP profile, e.g., RFC 3551 [7].  If
 best-effort service is being used, users of this payload format SHALL
 monitor packet loss to ensure that the packet loss rate is within
 acceptable parameters.

6. Payload Format Parameters

 This RTP payload format is identified using the H264-RCDO media
 subtype, which is registered in accordance with RFC 4855 [10], and
 using the template of RFC 4288 [13].

Kristensen & Luthi Standards Track [Page 3] RFC 6185 H.264 RCDO RTP Payload May 2011

6.1. Media Type Definition

    Informative note: The media subtype definition for H264-RCDO is
    based on the definition of the H264 media subtype as specified in
    Section 8.1 of RFC 6184 [1].  Except for the profile-level-id
    parameter, for which new semantics are specified below, the
    optional parameters are copied from RFC 6184 [1] in order to
    provide a complete, self-contained media subtype registration to
    IANA.  The references are updated to match the numbering used in
    this document.
 The media subtype for RCDO for H.264 has been allocated from the IETF
 tree.
 Type name: video
 Subtype name: H264-RCDO
 Required parameters:
 rate:  Indicates the RTP timestamp clock rate.  The rate value MUST
    be 90000.
 Optional parameters:
 profile-level-id:  A base16 RFC 4648 [9] (hexadecimal) representation
    of the following three bytes in the sequence parameter set NAL
    unit is specified in H.264 [2]: 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 [2], 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 receiver supports.
    RCDO is distinct from any profile; this implies that the profile
    value 0 (no profile) and the profile_idc byte of the profile-
    level-id parameter are equal to 0.  An RCDO bitstream MUST obey
    all the constraints of the Baseline profile.  Therefore, only
    constraint_set0_flag is equal to 1 in the profile-iop part of the
    profile-level-id parameter; the remaining bits are set to 0.

Kristensen & Luthi Standards Track [Page 4] RFC 6185 H.264 RCDO RTP Payload May 2011

    If the profile-level-id parameter is used to indicate properties
    of a NAL unit stream, 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 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.
    For example, if a codec supports level 1.3, the profile-level-id
    becomes 00800d, in which 00 indicates the "no profile" value, 80
    indicates the constraints of the Baseline profile, and 0d
    indicates level 1.3.  When level 2.1 is supported, the profile-
    level-id becomes 008015.
    If no profile-level-id is present, level 1 (i.e., equivalent to
    profile-level-id 00800a) MUST be implied.
       Informative note: The definitions of the remaining optional
       parameters below are copied verbatim from Section 8.1 of RFC
       6184 [1].  Only the references are updated to match the
       numbering used in this document.
 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 [2]: 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 if 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.

Kristensen & Luthi Standards Track [Page 5] RFC 6185 H.264 RCDO RTP Payload May 2011

 max-mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br:  These
    parameters MAY be used to signal the capabilities of a receiver
    implementation.  These parameters MUST NOT be used for any other
    purpose.  The highest level conveyed in the value of the profile-
    level-id parameter or the max-recv-level parameter MUST be such
    that the receiver is fully capable of supporting. max-mbps, max-
    smbps, max-fs, max-cpb, max-dpb, and max-br MAY be used to
    indicate capabilities of the receiver that extend the required
    capabilities of the signaled highest level, as specified below.
    When more than one parameter from the set (max-mbps, max-smbps,
    max-fs, max-cpb, max-dpb, max-br) is present, the receiver MUST
    support all signaled capabilities simultaneously.  For example, if
    both max-mbps and max-br are present, the signaled highest level
    with the extension of both the frame rate and bitrate is
    supported.  That is, the receiver is able to decode NAL unit
    streams in which the macroblock processing rate is up to max-mbps
    (inclusive), the bitrate is up to max-br (inclusive), the coded
    picture buffer size is derived as specified in the semantics of
    the max-br parameter below, and the other properties comply with
    the highest level specified in the value of the profile-level-id
    parameter or the max-recv-level parameter.
    If a receiver can support all the properties of Level A, the
    highest level specified in the value of the profile-level-id
    parameter or the max-recv-level parameter MUST be Level A (i.e.,
    MUST NOT be lower than Level A).  In other words, a receiver MUST
    NOT signal values of max-mbps, max-fs, max-cpb, max-dpb, and
    max-br that taken together meet the requirements of a higher level
    compared to the highest level specified in the value of the
    profile-level-id parameter or the max-recv-level parameter.
       Informative note: When the OPTIONAL media type parameters are
       used to signal the properties of a NAL unit stream, max-mbps,
       max-smbps, max-fs, max-cpb, max-dpb, and max-br are not
       present, and the value of profile-level-id must always be such
       that the NAL unit stream complies fully with the specified
       profile and level.
 max-mbps:  The value of max-mbps is an integer indicating the maximum
    macroblock processing rate in units of macroblocks per second.
    The max-mbps parameter signals that the receiver is capable of
    decoding video at a higher rate 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-mbps is
    signaled, the receiver MUST be able to decode NAL unit streams
    that conform to the signaled highest level, with the exception
    that the MaxMBPS value in Table A-1 of H.264 [2] for the signaled

Kristensen & Luthi Standards Track [Page 6] RFC 6185 H.264 RCDO RTP Payload May 2011

    highest level is replaced with the value of max-mbps.  The value
    of max-mbps MUST be greater than or equal to the value of MaxMBPS
    given in Table A-1 of H.264 [2] for the highest level.  Senders
    MAY use this knowledge to send pictures of a given size at a
    higher picture rate than is indicated in the signaled highest
    level.
 max-smbps:  The value of max-smbps is an integer indicating the
    maximum static macroblock processing rate in units of static
    macroblocks per second, under the hypothetical assumption that all
    macroblocks are static macroblocks.  When max-smbps is signaled,
    the MaxMBPS value in Table A-1 of H.264 [2] should be replaced
    with the result of the following computation:
    o If the parameter max-mbps is signaled, set a variable
      MaxMacroblocksPerSecond to the value of max-mbps.  Otherwise,
      set MaxMacroblocksPerSecond equal to the value of MaxMBPS in
      Table A-1 of H.264 [2] for the signaled highest level conveyed
      in the value of the profile-level-id parameter or the
      max-recv-level parameter.
    o Set a variable P_non-static to the proportion of non-static
      macroblocks in picture n.
    o Set a variable P_static to the proportion of static macroblocks
      in picture n.
    o The value of MaxMBPS in Table A-1 of H.264 [2] should be
      considered by the encoder to be equal to:
       MaxMacroblocksPerSecond * max-smbps / (P_non-static * max-smbps
       + P_static * MaxMacroblocksPerSecond)
    The encoder should recompute this value for each picture.  The
    value of max-smbps MUST be greater than or equal to the value of
    MaxMBPS given explicitly as the value of the max-mbps parameter or
    implicitly in Table A-1 of H.264 [2] for the signaled highest
    level.  Senders MAY use this knowledge to send pictures of a given
    size at a higher picture rate than is indicated in the signaled
    highest level.
 max-fs:  The value of max-fs is an integer indicating the maximum
    frame size in units of macroblocks.  The max-fs parameter signals
    that the receiver is capable of decoding larger picture sizes than
    are required by the signaled highest level conveyed in the value
    of the profile-level-id parameter or the max-recv-level parameter.
    When max-fs is signaled, the receiver MUST be able to decode NAL
    unit streams that conform to the signaled highest level, with the

Kristensen & Luthi Standards Track [Page 7] RFC 6185 H.264 RCDO RTP Payload May 2011

    exception that the MaxFS value in Table A-1 of H.264 [2] for the
    signaled highest level is replaced with the value of max-fs.  The
    value of max-fs MUST be greater than or equal to the value of
    MaxFS given in Table A-1 of H.264 [2] for the highest level.
    Senders MAY use this knowledge to send larger pictures at a
    proportionally lower frame rate than is indicated in the signaled
    highest level.
 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 [2]).  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 [2] 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
    [2] 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
    [2].
       Informative note: The coded picture buffer is used in the
       hypothetical reference decoder (Annex C of H.264).  The use of
       the hypothetical reference decoder is recommended in H.264
       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
       and de-jitter buffers.  The coded picture buffer need not be
       implemented in decoders as specified in Annex C of H.264, but
       rather standard-compliant decoders can have any buffering
       arrangements provided that they can decode standard-compliant
       bitstreams.  Thus, in practice, the input buffer for a video
       decoder can be integrated with de-interleaving and de-jitter
       buffers of the receiver.

Kristensen & Luthi Standards Track [Page 8] RFC 6185 H.264 RCDO RTP Payload May 2011

 max-dpb:  The value of max-dpb is an integer indicating the maximum
    decoded picture buffer size in units of 8/3 macroblocks.  The max-
    dpb parameter signals that the receiver has more memory than the
    minimum amount of decoded 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-dpb is signaled, the receiver MUST be able to decode NAL unit
    streams that conform to the signaled highest level, with the
    exception that the MaxDpbMbs value in Table A-1 of H.264 [2] for
    the signaled highest level is replaced with the value of max-dpb *
    3 / 8.  Consequently, a receiver that signals max-dpb MUST be
    capable of storing the following number of decoded frames,
    complementary field pairs, and non-paired fields in its decoded
    picture buffer:
       Min(max-dpb * 3 / 8 / ( PicWidthInMbs * FrameHeightInMbs), 16)
    Wherein PicWidthInMbs and FrameHeightInMbs are defined in H.264
    [2].
    The value of max-dpb MUST be greater than or equal to the value of
    MaxDpbMbs * 3 / 8, wherein the value of MaxDpbMbs is given in
    Table A-1 of H.264 [2] for the highest level.  Senders MAY use
    this knowledge to construct coded video streams with improved
    compression.
       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.  The
       decoded picture buffer stores reconstructed samples.  There is
       no relationship between the size of the decoded picture buffer
       and the buffers used in RTP, especially de-interleaving and
       de-jitter buffers.
       Informative note: In RFC 3984, which is obsoleted by RFC 6184,
       the unit of this parameter was 1024 bytes.  The unit has been
       changed to 8/3 macroblocks in this document.  The reason for
       this change was due to the changes from the 2003 version of the
       H.264 specification referenced by RFC 3984 to the 2010 version
       of the H.264 specification referenced by this document,
       particularly the changes to Table A-1 in the H.264
       specification due to addition of color formats and bit depths
       not supported earlier.  The changed semantics of this parameter
       keeps backward compatibility to RFC 3984 and supports all
       profiles defined in the 2010 version of the H.264
       specification.

Kristensen & Luthi Standards Track [Page 9] RFC 6185 H.264 RCDO RTP Payload May 2011

 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 [2]).
    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 [2] 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 [2]: (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 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 [2]
    for the signaled highest level.
    Senders MAY use this knowledge to send higher bitrate video as
    allowed in the level definition of Annex A of H.264 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.  The
       assumption that the network is capable of handling such
       bitrates at any given time cannot be made from the value of
       this parameter.  In particular, no conclusion can be drawn that
       the signaled bitrate is possible under congestion control
       constraints.

Kristensen & Luthi Standards Track [Page 10] RFC 6185 H.264 RCDO RTP Payload May 2011

 redundant-pic-cap:  This parameter signals the capabilities of a
    receiver implementation.  When equal to 0, the parameter indicates
    that the receiver makes no attempt to use redundant coded pictures
    to correct incorrectly decoded primary coded pictures.  When equal
    to 0, the receiver is not capable of using redundant slices;
    therefore, a sender SHOULD avoid sending redundant slices to save
    bandwidth.  When equal to 1, the receiver is capable of decoding
    any such redundant slice that covers a corrupted area in a primary
    decoded picture (at least partly), and therefore a sender MAY send
    redundant slices.  When the parameter is not present, a value of 0
    MUST be used for redundant-pic-cap.  When present, the value of
    redundant-pic-cap MUST be either 0 or 1.
    When the profile-level-id parameter is present in the same
    signaling as the redundant-pic-cap parameter and the profile
    indicated in profile-level-id is such that it disallows the use of
    redundant coded pictures (e.g., Main profile), the value of
    redundant-pic-cap MUST be equal to 0.  When a receiver indicates
    redundant-pic-cap equal to 0, the received stream SHOULD NOT
    contain redundant coded pictures.
       Informative note: Even if redundant-pic-cap is equal to 0, the
       decoder is able to ignore redundant codec pictures provided
       that the decoder supports a profile (Baseline, Extended) in
       which redundant coded pictures are allowed.
       Informative note: Even if redundant-pic-cap is equal to 1, the
       receiver may also choose other error concealment strategies to
       replace or complement decoding of redundant slices.
 sprop-parameter-sets:  This parameter MAY be used to convey any
    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.
    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 RFC 4648 [9] representations
    of parameter set NAL units as specified in Sections 7.3.2.1 and
    7.3.2.2 of H.264 [2].  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 hundred bytes.
       Informative note: When several payload types are offered in the
       SDP Offer/Answer model, each with its own sprop-parameter-sets
       parameter, the receiver cannot assume that those parameter sets
       do not use conflicting storage locations (i.e., identical
       values of parameter set identifiers).  Therefore, a receiver

Kristensen & Luthi Standards Track [Page 11] RFC 6185 H.264 RCDO RTP Payload May 2011

       should buffer all sprop-parameter-sets and make them available
       to the decoder instance that decodes a certain payload type.
    The sprop-parameter-sets parameter MUST only contain parameter
    sets that are conforming to the profile-level-id, i.e., the subset
    of coding tools indicated by any of the parameter sets MUST be
    equal to the default sub-profile, and the level indicated by any
    of the parameter sets MUST be equal to the default level.
 sprop-level-parameter-sets:  This parameter MAY be used to convey any
    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.  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 associated with one level 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 one 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
    RFC 4648 [9] representation of the initial parameter set NAL units
    for the level.  Each pair of PLId:PSLs 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.  All sequence
    parameter sets contained in each PSL MUST have the three bytes
    from profile_idc to level_idc, inclusive, equal to the preceding
    PLId.
       Informative note: This parameter allows for efficient level
       downgrade or upgrade in SDP Offer/Answer and out-of-band
       transport of parameter sets simultaneously.
 use-level-src-parameter-sets:  This parameter MAY be used to indicate
    a receiver capability.  The value MAY be equal to either 0 or 1.
    When the parameter is not present, the value MUST be inferred to
    be equal to 0.  The value 0 indicates that the receiver does not
    understand the sprop-level-parameter-sets parameter, does not

Kristensen & Luthi Standards Track [Page 12] RFC 6185 H.264 RCDO RTP Payload May 2011

    understand the "fmtp" source attribute as specified in Section 6.3
    of RFC 5576 [14], will ignore sprop-level-parameter-sets when
    present, and will ignore sprop-parameter-sets when conveyed using
    the "fmtp" source attribute.  The value 1 indicates that the
    receiver understands the sprop-level-parameter-sets parameter,
    understands the "fmtp" source attribute as specified in Section
    6.3 of RFC 5576 [14], and is capable of using parameter sets
    contained in the sprop-level-parameter-sets or contained in the
    sprop-parameter-sets that is conveyed using the "fmtp" source
    attribute.
       Informative note: An RFC 3984 receiver does not understand
       sprop-level-parameter-sets, use-level-src-parameter-sets, or
       the "fmtp" source attribute as specified in Section 6.3 of RFC
       5576 [14].  Therefore, during SDP Offer/Answer, an RFC 3984
       receiver as the answerer will simply ignore sprop-level-
       parameter-sets when present in an offer and sprop-parameter-
       sets conveyed using the "fmtp" source attribute, as specified
       in Section 6.3 of RFC 5576 [14].  Assume that the offered
       payload type was accepted at a level lower than the default
       level.  If the offered payload type included sprop-level-
       parameter-sets or included sprop-parameter-sets conveyed using
       the "fmtp" source attribute and if the offerer sees that the
       answerer has not included use-level-src-parameter-sets equal to
       1 in the answer, the offerer knows that in-band transport of
       parameter sets is needed.
 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 send parameter sets in-band.  When in-band-parameter-
    sets is equal to 1, use-level-src-parameter-sets MUST NOT be
    present or MUST be equal to 0.  When the parameter is not present,
    this receiver capability is not specified, and therefore the
    sender MAY send out-of-band parameter sets only, it MAY send in-
    band-parameter-sets only, or it MAY send both.
 level-asymmetry-allowed:  This parameter MAY be used in SDP Offer/
    Answer to indicate whether level asymmetry, i.e., sending media
    encoded at a different level in the offerer-to-answerer direction
    than the level in the answerer-to-offerer direction, is allowed.
    The value MAY be equal to either 0 or 1.  When the parameter is
    not present, the value MUST be inferred to be equal to 0.  The

Kristensen & Luthi Standards Track [Page 13] RFC 6185 H.264 RCDO RTP Payload May 2011

    value 1 in both the offer and the answer indicates that level
    asymmetry is allowed.  The value of 0 in either the offer or the
    answer indicates that level asymmetry is not allowed.
    If level-asymmetry-allowed is equal to 0 (or not present) in
    either the offer or the answer, level asymmetry is not allowed.
    In this case, the level to use in the direction from the offerer
    to the answerer MUST be the same as the level to use in the
    opposite direction.
 packetization-mode:  This parameter signals the properties of an RTP
    payload type or the capabilities of a receiver implementation.
    Only a single configuration point can be indicated; thus, when
    capabilities to support more than one packetization-mode are
    declared, multiple configuration points (RTP payload types) must
    be used.
    When the value of packetization-mode is equal to 0 or
    packetization-mode is not present, the single NAL mode MUST be
    used.  This mode is in use in standards using ITU-T Recommendation
    H.241 [3] (see Section 12.1).  When the value of packetization-
    mode is equal to 1, the non-interleaved mode MUST be used.  When
    the value of packetization-mode is equal to 2, the interleaved
    mode MUST be used.  The value of packetization-mode MUST be an
    integer in the range of 0 to 2, inclusive.
 sprop-interleaving-depth:  This parameter MUST NOT be present when
    packetization-mode is not present or the value of packetization-
    mode is equal to 0 or 1.  This parameter MUST be present when the
    value of packetization-mode is equal to 2.
    This parameter signals the properties of an RTP packet stream.  It
    specifies the maximum number of VCL NAL units that precede any VCL
    NAL unit in the RTP packet stream in transmission order and that
    follow the VCL NAL unit in decoding order.  Consequently, it is
    guaranteed that receivers can reconstruct NAL unit decoding order
    when the buffer size for NAL unit decoding order recovery is at
    least the value of sprop-interleaving-depth + 1 in terms of VCL
    NAL units.
    The value of sprop-interleaving-depth MUST be an integer in the
    range of 0 to 32767, inclusive.
 sprop-deint-buf-req:  This parameter MUST NOT be present when
    packetization-mode is not present or the value of packetization-
    mode is equal to 0 or 1.  It MUST be present when the value of
    packetization-mode is equal to 2.

Kristensen & Luthi Standards Track [Page 14] RFC 6185 H.264 RCDO RTP Payload May 2011

    sprop-deint-buf-req signals the required size of the
    de-interleaving buffer for the RTP packet stream.  The value of
    the parameter MUST be greater than or equal to the maximum buffer
    occupancy (in units of bytes) required in such a de-interleaving
    buffer that is specified in Section 7.2 of RFC 6184 [1].  It is
    guaranteed that receivers can perform the de-interleaving of
    interleaved NAL units into NAL unit decoding order, when the
    de-interleaving buffer size is at least the value of
    sprop-deint-buf-req in terms of bytes.
    The value of sprop-deint-buf-req MUST be an integer in the range
    of 0 to 4294967295, inclusive.
       Informative note: sprop-deint-buf-req indicates the required
       size of the de-interleaving buffer only.  When network jitter
       can occur, an appropriately sized jitter buffer has to be
       provisioned for as well.
 deint-buf-cap:  This parameter signals the capabilities of a receiver
    implementation and indicates the amount of de-interleaving buffer
    space in units of bytes that the receiver has available for
    reconstructing the NAL unit decoding order.  A receiver is able to
    handle any stream for which the value of the sprop-deint-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 deint-buf-cap.  The value of deint-buf-cap MUST be an integer
    in the range of 0 to 4294967295, inclusive.
       Informative note: deint-buf-cap indicates the maximum possible
       size of the de-interleaving buffer of the receiver only.  When
       network jitter can occur, an appropriately sized jitter buffer
       has to be provisioned for as well.
 sprop-init-buf-time:  This parameter MAY be used to signal the
    properties of an RTP packet stream.  The parameter MUST NOT be
    present if the value of packetization-mode is equal to 0 or 1.
    The parameter signals the initial buffering time that a receiver
    MUST wait before starting decoding to recover the NAL unit
    decoding order from the transmission order.  The parameter is the
    maximum value of (decoding time of the NAL unit - transmission
    time of a NAL unit), assuming reliable and instantaneous
    transmission, the same timeline for transmission and decoding, and
    commencement of decoding when the first packet arrives.
    An example of specifying the value of sprop-init-buf-time follows.
    A NAL unit stream is sent in the following interleaved order, in

Kristensen & Luthi Standards Track [Page 15] RFC 6185 H.264 RCDO RTP Payload May 2011

    which the value corresponds to the decoding time and the
    transmission order is from left to right:
       0 2 1 3 5 4 6 8 7 ...
    Assuming a steady transmission rate of NAL units, the transmission
    times are:
       0 1 2 3 4 5 6 7 8 ...
    Subtracting the decoding time from the transmission time column-
    wise results in the following series:
       0 -1 1 0 -1 1 0 -1 1 ...
    Thus, in terms of intervals of NAL unit transmission times, the
    value of sprop-init-buf-time in this example is 1.  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-init-buf-time MUST be an integer in the range of 0 to
    4294967295, inclusive.
    In addition to the signaled sprop-init-buf-time, receivers SHOULD
    take into account the transmission delay jitter buffering,
    including buffering for the delay jitter caused by mixers,
    translators, gateways, proxies, traffic-shapers, and other network
    elements.
 sprop-max-don-diff:  This parameter MAY be used to signal the
    properties of an RTP packet stream.  It MUST NOT be used to signal
    transmitter, receiver, or codec capabilities.  The parameter MUST
    NOT be present if the value of packetization-mode is equal to 0 or
    1. sprop-max-don-diff is an integer in the range of 0 to 32767,
    inclusive.  If sprop-max-don-diff is not present, the value of the
    parameter is unspecified. sprop-max-don-diff is calculated as
    follows:
       sprop-max-don-diff = max{AbsDON(i) - AbsDON(j)}, for any i and
       any j>i,
    where i and j indicate the index of the NAL unit in the
    transmission order and AbsDON denotes a decoding order number of
    the NAL unit that does not wrap around to 0 after 65535.  In other
    words, AbsDON is calculated as follows: let m and n be consecutive
    NAL units in transmission order.  For the very first NAL unit in
    transmission order (whose index is 0), AbsDON(0) = DON(0).  For
    other NAL units, AbsDON is calculated as follows:

Kristensen & Luthi Standards Track [Page 16] RFC 6185 H.264 RCDO RTP Payload May 2011

    If DON(m) == DON(n), AbsDON(n) = AbsDON(m)
    If (DON(m) < DON(n) and DON(n) - DON(m) < 32768),
    AbsDON(n) = AbsDON(m) + DON(n) - DON(m)
    If (DON(m) > DON(n) and DON(m) - DON(n) >= 32768),
    AbsDON(n) = AbsDON(m) + 65536 - DON(m) + DON(n)
    If (DON(m) < DON(n) and DON(n) - DON(m) >= 32768),
    AbsDON(n) = AbsDON(m) - (DON(m) + 65536 - DON(n))
    If (DON(m) > DON(n) and DON(m) - DON(n) < 32768),
    AbsDON(n) = AbsDON(m) - (DON(m) - DON(n))
    where DON(i) is the decoding order number of the NAL unit having
    index i in the transmission order.  The decoding order number is
    specified in Section 5.5 of RFC 6184 [1].
       Informative note: Receivers may use sprop-max-don-diff to
       trigger which NAL units in the receiver buffer can be passed to
       the decoder.
 max-rcmd-nalu-size:  This parameter MAY be used to signal the
    capabilities of a receiver.  The parameter MUST NOT be used for
    any other purposes.  The value of the parameter indicates the
    largest NALU size in bytes that the receiver can handle
    efficiently.  The parameter value is a recommendation, not a
    strict upper boundary.  The sender MAY create larger NALUs but
    must be aware that the handling of these may come at a higher cost
    than NALUs conforming to the limitation.
    The value of max-rcmd-nalu-size MUST be an integer in the range of
    0 to 4294967295, inclusive.  If this parameter is not specified,
    no known limitation to the NALU size exists.  Senders still have
    to consider the MTU size available between the sender and the
    receiver and SHOULD run MTU discovery for this purpose.
    This parameter is motivated by, for example, an IP to H.223 video
    telephony gateway, where NALUs smaller than the H.223 transport
    data unit will be more efficient.  A gateway may terminate IP;
    thus, MTU discovery will normally not work beyond the gateway.
       Informative note: Setting this parameter to a lower than
       necessary value may have a negative impact.

Kristensen & Luthi Standards Track [Page 17] RFC 6185 H.264 RCDO RTP Payload May 2011

 sar-understood:  This parameter MAY be used to indicate a receiver
    capability and nothing else.  The parameter indicates the maximum
    value of aspect_ratio_idc (specified in H.264 [2]) smaller than
    255 that the receiver understands.  Table E-1 of H.264 [2]
    specifies aspect_ratio_idc equal to 0 as "unspecified"; 1 to 16,
    inclusive, as specific Sample Aspect Ratios (SARs); 17 to 254,
    inclusive, as "reserved"; and 255 as the Extended SAR, for which
    SAR width and SAR height are explicitly signaled.  Therefore, a
    receiver with a decoder according to H.264 [2] understands
    aspect_ratio_idc in the range of 1 to 16, inclusive, and
    aspect_ratio_idc equal to 255, in the sense that the receiver
    knows exactly what the SAR is.  For such a receiver, the value of
    sar-understood is 16.  In the future, if Table E-1 of H.264 [2] is
    extended, e.g., such that the SAR for aspect_ratio_idc equal to 17
    is specified, then for a receiver with a decoder that understands
    the extension, the value of sar-understood is 17.  For a receiver
    with a decoder according to the 2003 version of H.264 [2], the
    value of sar-understood is 13, as the minimum reserved
    aspect_ratio_idc therein is 14.
    When sar-understood is not present, the value MUST be inferred to
    be equal to 13.
 sar-supported:  This parameter MAY be used to indicate a receiver
    capability and nothing else.  The value of this parameter is an
    integer in the range of 1 to sar-understood, inclusive, equal to
    255.  The value of sar-supported equal to N smaller than 255
    indicates that the receiver supports all the SARs corresponding to
    H.264 aspect_ratio_idc values (see Table E-1 of H.264 [2]) in the
    range from 1 to N, inclusive, without geometric distortion.  The
    value of sar-supported equal to 255 indicates that the receiver
    supports all sample aspect ratios that are expressible using two
    16-bit integer values as the numerator and denominator, i.e.,
    those that are expressible using the H.264 aspect_ratio_idc value
    of 255 (Extended_SAR, see Table E-1 of H.264 [2]), without
    geometric distortion.
    H.264-compliant encoders SHOULD NOT send an aspect_ratio_idc equal
    to 0 or an aspect_ratio_idc larger than sar-understood and smaller
    than 255.  H.264-compliant encoders SHOULD send an
    aspect_ratio_idc that the receiver is able to display without
    geometrical distortion.  However, H.264-compliant encoders MAY
    choose to send pictures using any SAR.
    Note that the actual sample aspect ratio or extended sample aspect
    ratio, when present, of the stream is conveyed in the Video
    Usability Information (VUI) part of the sequence parameter set.

Kristensen & Luthi Standards Track [Page 18] RFC 6185 H.264 RCDO RTP Payload May 2011

 Encoding considerations:  This type is only defined for transfer via
    RTP (RFC 3550) and is framed and binary (see Section 4.8 in RFC
    4288).
 Security considerations:  See Section 9 of RFC 6185.
 Interoperability considerations:  None
 Published specification:  RFC 6185 and its reference section
 Applications that use this media type:  Video streaming and
    conferencing applications
 Additional information:  None
    Magic number(s):
    File extension(s):
    Macintosh file type code(s):
 Person & email address to contact for further information:
    Tom Kristensen <tom.kristensen@tandberg.com>, <tomkri@ifi.uio.no>
 Intended usage:  COMMON
 Restrictions on usage:  This type depends on RTP framing; hence, it
    is only defined for transfer via RTP (see RFC 3550).  Transport
    within other framing protocols is not defined at this time.
 Author:  Tom Kristensen
 Change controller:  IETF Audio/Video Transport Working Group
    delegated from the IESG

7. Mapping to SDP

 The mapping of the above defined payload format media subtype and its
 parameters SHALL be done according to Section 3 of RFC 4855 [10].
 An example of the "fmtp" attribute in the media representation of a
 level 2.2 bitstream is as follows:
    a=fmtp:97 profile-level-id=008016

Kristensen & Luthi Standards Track [Page 19] RFC 6185 H.264 RCDO RTP Payload May 2011

7.1. Offer/Answer Considerations

 When H264-RCDO is offered over RTP using SDP in an Offer/Answer model
 [5] for unicast and multicast usage, the limitations and rules
 described in Section 8.2.2 of RFC 6184 [1] apply.  Note that the
 profile_idc byte of the H264-RCDO profile-level-id parameter can only
 take the value of 0 (no profile).
 For interoperability with systems not supporting H264-RCDO, it is
 RECOMMENDED to offer the H264 media subtype as well.  As specified in
 RFC 3264 [5], listing the payload number for H264-RCDO before H264 in
 the format list on the "m=" line signals that H264-RCDO is preferred
 over H264.  Following is an example where this scheme is applied:
    m=video 5555 RTP/AVP 97 98
    a=rtpmap:97 H264-RCDO/90000
    a=fmtp:97 profile-level-id=008016;max-mbps=42000;max-smbps=323500
    a=rtpmap:98 H264/90000
    a=fmtp:98 profile-level-id=428016;max-mbps=35000;max-smbps=323500

7.2. Declarative SDP Considerations

 When H264-RCDO over RTP is offered with SDP in a declarative style,
 as in the Real Time Streaming Protocol (RTSP) [11] or the Session
 Announcement Protocol (SAP) [12], the considerations in Section 8.2.3
 of RFC 6184 [1] apply.  Note that the profile_idc byte of the H264-
 RCDO profile-level-id parameter can only take the value of 0 (no
 profile).

8. IANA Considerations

 IANA has registered H264-RCDO as specified in Section 6.1.  The media
 subtype has also been added to the IANA registry for "RTP Payload
 Format MIME types" (http://www.iana.org).

9. Security Considerations

 RTP packets using the payload format defined in this specification
 are subject to the security considerations discussed in the RTP
 specification [6] and in any applicable RTP profile.  Refer also to
 the security considerations of the RTP Payload Format for H.264 Video
 specification in RFC 6184 [1].  No additional security considerations
 are introduced by this specification.

Kristensen & Luthi Standards Track [Page 20] RFC 6185 H.264 RCDO RTP Payload May 2011

10. Acknowledgements

 The authors would like to acknowledge Gisle Bjoentegaard and Arild
 Fuldseth for their technical contribution to the specification.  In
 the final phases, Roni Even did a helpful review.

11. References

11.1. Normative References

 [1]   Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP Payload
       Format for H.264 Video", RFC 6184, May 2011.
 [2]   International Telecommunications Union, "Advanced video coding
       for generic audiovisual services", ITU-T Recommendation H.264,
       March 2010.
 [3]   International Telecommunications Union, "Extended video
       procedures and control signals for H.300-series terminals",
       ITU-T Recommendation H.241, May 2006.
 [4]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.
 [5]   Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
       Session Description Protocol (SDP)", RFC 3264, June 2002.
 [6]   Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
       "RTP: A Transport Protocol for Real-Time Applications", STD 64,
       RFC 3550, July 2003.
 [7]   Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
       Conferences with Minimal Control", STD 65, RFC 3551, July 2003.
 [8]   Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
       Description Protocol", RFC 4566, July 2006.
 [9]   Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
       RFC 4648, October 2006.
 [10]  Casner, S., "Media Type Registration of RTP Payload Formats",
       RFC 4855, February 2007.

11.2. Informative References

 [11]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming
       Protocol (RTSP)", RFC 2326, April 1998.

Kristensen & Luthi Standards Track [Page 21] RFC 6185 H.264 RCDO RTP Payload May 2011

 [12]  Handley, M., Perkins, C., and E. Whelan, "Session Announcement
       Protocol", RFC 2974, October 2000.
 [13]  Freed, N. and J. Klensin, "Media Type Specifications and
       Registration Procedures", BCP 13, RFC 4288, December 2005.
 [14]  Lennox, J., Ott, J., and T. Schierl, "Source-Specific Media
       Attributes in the Session Description Protocol (SDP)",
       RFC 5576, June 2009.

Authors' Addresses

 Tom Kristensen
 TANDBERG
 Philip Pedersens vei 22
 N-1366 Lysaker
 Norway
 Phone: +47 67125125
 EMail: tom.kristensen@tandberg.com, tomkri@ifi.uio.no
 URI:   http://www.tandberg.com
 Patrick Luthi
 TANDBERG
 Philip Pedersens vei 22
 N-1366 Lysaker
 Norway
 EMail: patrick.luthi@tandberg.com
 URI:   http://www.tandberg.com

Kristensen & Luthi Standards Track [Page 22]

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