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rfc:rfc3016

Network Working Group Y. Kikuchi Request for Comments: 3016 Toshiba Category: Standards Track T. Nomura

                                                                   NEC
                                                           S. Fukunaga
                                                                   Oki
                                                             Y. Matsui
                                                            Matsushita
                                                             H. Kimata
                                                                   NTT
                                                         November 2000
         RTP Payload Format for MPEG-4 Audio/Visual Streams

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

 This document describes Real-Time Transport Protocol (RTP) payload
 formats for carrying each of MPEG-4 Audio and MPEG-4 Visual
 bitstreams without using MPEG-4 Systems.  For the purpose of directly
 mapping MPEG-4 Audio/Visual bitstreams onto RTP packets, it provides
 specifications for the use of RTP header fields and also specifies
 fragmentation rules.  It also provides specifications for
 Multipurpose Internet Mail Extensions (MIME) type registrations and
 the use of Session Description Protocol (SDP).

1. Introduction

 The RTP payload formats described in this document specify how MPEG-4
 Audio [3][5] and MPEG-4 Visual streams [2][4] are to be fragmented
 and mapped directly onto RTP packets.
 These RTP payload formats enable transport of MPEG-4 Audio/Visual
 streams without using the synchronization and stream management
 functionality of MPEG-4 Systems [6].  Such RTP payload formats will
 be used in systems that have intrinsic stream management

Kikuchi, et al. Standards Track [Page 1] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 functionality and thus require no such functionality from MPEG-4
 Systems.  H.323 terminals are an example of such systems, where
 MPEG-4 Audio/Visual streams are not managed by MPEG-4 Systems Object
 Descriptors but by H.245.  The streams are directly mapped onto RTP
 packets without using MPEG-4 Systems Sync Layer.  Other examples are
 SIP and RTSP where MIME and SDP are used.  MIME types and SDP usages
 of the RTP payload formats described in this document are defined to
 directly specify the attribute of Audio/Visual streams (e.g., media
 type, packetization format and codec configuration) without using
 MPEG-4 Systems.  The obvious benefit is that these MPEG-4
 Audio/Visual RTP payload formats can be handled in an unified way
 together with those formats defined for non-MPEG-4 codecs.  The
 disadvantage is that interoperability with environments using MPEG-4
 Systems may be difficult, other payload formats may be better suited
 to those applications.
 The semantics of RTP headers in such cases need to be clearly
 defined, including the association with MPEG-4 Audio/Visual data
 elements.  In addition, it is beneficial to define the fragmentation
 rules of RTP packets for MPEG-4 Video streams so as to enhance error
 resiliency by utilizing the error resilience tools provided inside
 the MPEG-4 Video stream.

1.1 MPEG-4 Visual RTP payload format

 MPEG-4 Visual is a visual coding standard with many new features:
 high coding efficiency; high error resiliency; multiple, arbitrary
 shape object-based coding; etc. [2].  It covers a wide range of
 bitrates from scores of Kbps to several Mbps.  It also covers a wide
 variety of networks, ranging from those guaranteed to be almost
 error-free to mobile networks with high error rates.
 With respect to the fragmentation rules for an MPEG-4 Visual
 bitstream defined in this document, since MPEG-4 Visual is used for a
 wide variety of networks, it is desirable not to apply too much
 restriction on fragmentation, and a fragmentation rule such as "a
 single video packet shall always be mapped on a single RTP packet"
 may be inappropriate.  On the other hand, careless, media unaware
 fragmentation may cause degradation in error resiliency and bandwidth
 efficiency.  The fragmentation rules described in this document are
 flexible but manage to define the minimum rules for preventing
 meaningless fragmentation while utilizing the error resilience
 functionalities of MPEG-4 Visual.
 The fragmentation rule recommends not to map more than one VOP in an
 RTP packet so that the RTP timestamp uniquely indicates the VOP time
 framing.  On the other hand, MPEG-4 video may generate VOPs of very
 small size, in cases with an empty VOP (vop_coded=0) containing only

Kikuchi, et al. Standards Track [Page 2] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 VOP header or an arbitrary shaped VOP with a small number of coding
 blocks.  To reduce the overhead for such cases, the fragmentation
 rule permits concatenating multiple VOPs in an RTP packet.  (See
 fragmentation rule (4) in section 3.2 and marker bit and timestamp in
 section 3.1.)
 While the additional media specific RTP header defined for such video
 coding tools as H.261 or MPEG-1/2 is effective in helping to recover
 picture headers corrupted by packet losses, MPEG-4 Visual has already
 error resilience functionalities for recovering corrupt headers, and
 these can be used on RTP/IP networks as well as on other networks
 (H.223/mobile, MPEG-2/TS, etc.).  Therefore, no extra RTP header
 fields are defined in this MPEG-4 Visual RTP payload format.

1.2 MPEG-4 Audio RTP payload format

 MPEG-4 Audio is a new kind of audio standard that integrates many
 different types of audio coding tools.  Low-overhead MPEG-4 Audio
 Transport Multiplex (LATM) manages the sequences of audio data with
 relatively small overhead.  In audio-only applications, then, it is
 desirable for LATM-based MPEG-4 Audio bitstreams to be directly
 mapped onto the RTP packets without using MPEG-4 Systems.
 While LATM has several multiplexing features as follows;
  1. Carrying configuration information with audio data,
  2. Concatenation of multiple audio frames in one audio stream,
  3. Multiplexing multiple objects (programs),
  4. Multiplexing scalable layers,
 in RTP transmission there is no need for the last two features.
 Therefore, these two features MUST NOT be used in applications based
 on RTP packetization specified by this document.  Since LATM has been
 developed for only natural audio coding tools, i.e., not for
 synthesis tools, it seems difficult to transmit Structured Audio (SA)
 data and Text to Speech Interface (TTSI) data by LATM.  Therefore, SA
 data and TTSI data MUST NOT be transported by the RTP packetization
 in this document.
 For transmission of scalable streams, audio data of each layer SHOULD
 be packetized onto different RTP packets allowing for the different
 layers to be treated differently at the IP level, for example via
 some means of differentiated service.  On the other hand, all
 configuration data of the scalable streams are contained in one LATM
 configuration data "StreamMuxConfig" and every scalable layer shares
 the StreamMuxConfig.  The mapping between each layer and its
 configuration data is achieved by LATM header information attached to

Kikuchi, et al. Standards Track [Page 3] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 the audio data.  In order to indicate the dependency information of
 the scalable streams, a restriction is applied to the dynamic
 assignment rule of payload type (PT) values (see section 4.2).
 For MPEG-4 Audio coding tools, as is true for other audio coders, if
 the payload is a single audio frame, packet loss will not impair the
 decodability of adjacent packets.  Therefore, the additional media
 specific header for recovering errors will not be required for MPEG-4
 Audio.  Existing RTP protection mechanisms, such as Generic Forward
 Error Correction (RFC 2733) and Redundant Audio Data (RFC 2198), MAY
 be applied to improve error resiliency.

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 RFC-2119 [7].

3. RTP Packetization of MPEG-4 Visual bitstream

 This section specifies RTP packetization rules for MPEG-4 Visual
 content.  An MPEG-4 Visual bitstream is mapped directly onto RTP
 packets without the addition of extra header fields or any removal of
 Visual syntax elements.  The Combined Configuration/Elementary stream
 mode MUST be used so that configuration information will be carried
 to the same RTP port as the elementary stream.  (see 6.2.1 "Start
 codes" of ISO/IEC 14496-2 [2][9][4]) The configuration information
 MAY additionally be specified by some out-of-band means.  If needed
 for an H.323 terminal, H.245 codepoint
 "decoderConfigurationInformation" MUST be used for this purpose.  If
 needed by systems using MIME content type and SDP parameters, e.g.,
 SIP and RTSP, the optional parameter "config" MUST be used to specify
 the configuration information (see 5.1 and 5.2).
 When the short video header mode is used, the RTP payload format for
 H.263 SHOULD be used (the format defined in RFC 2429 is RECOMMENDED,
 but the RFC 2190 format MAY be used for compatibility with older
 implementations).

Kikuchi, et al. Standards Track [Page 4] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

V=2PX CC M PT sequence number

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

timestamp

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

synchronization source (SSRC) identifier

+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+

contributing source (CSRC) identifiers
….

+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+

MPEG-4 Visual stream (byte aligned)
:…OPTIONAL RTP padding

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 1 - An RTP packet for MPEG-4 Visual stream

3.1 Use of RTP header fields for MPEG-4 Visual

 Payload Type (PT): The assignment of an RTP payload type for this new
 packet format is outside the scope of this document, and will not be
 specified here.  It is expected that the RTP profile for a particular
 class of applications will assign a payload type for this encoding,
 or if that is not done then a payload type in the dynamic range SHALL
 be chosen by means of an out of band signaling protocol (e.g., H.245,
 SIP, etc).
 Extension (X) bit: Defined by the RTP profile used.
 Sequence Number: Incremented by one for each RTP data packet sent,
 starting, for security reasons, with a random initial value.
 Marker (M) bit: The marker bit is set to one to indicate the last RTP
 packet (or only RTP packet) of a VOP.  When multiple VOPs are carried
 in the same RTP packet, the marker bit is set to one.
 Timestamp: The timestamp indicates the sampling instance of the VOP
 contained in the RTP packet.  A constant offset, which is random, is
 added for security reasons.
  1. When multiple VOPs are carried in the same RTP packet, the

timestamp indicates the earliest of the VOP times within the VOPs

    carried in the RTP packet.  Timestamp information of the rest of

Kikuchi, et al. Standards Track [Page 5] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

    the VOPs are derived from the timestamp fields in the VOP header
    (modulo_time_base and vop_time_increment).
 -  If the RTP packet contains only configuration information and/or
    Group_of_VideoObjectPlane() fields, the timestamp of the next VOP
    in the coding order is used.
 -  If the RTP packet contains only visual_object_sequence_end_code
    information, the timestamp of the immediately preceding VOP in the
    coding order is used.
 The resolution of the timestamp is set to its default value of 90kHz,
 unless specified by an out-of-band means (e.g., SDP parameter or MIME
 parameter as defined in section 5).
 Other header fields are used as described in RFC 1889 [8].

3.2 Fragmentation of MPEG-4 Visual bitstream

 A fragmented MPEG-4 Visual bitstream is mapped directly onto the RTP
 payload without any addition of extra header fields or any removal of
 Visual syntax elements.  The Combined Configuration/Elementary
 streams mode is used.  The following rules apply for the
 fragmentation.
 In the following, header means one of the following:
  1. Configuration information (Visual Object Sequence Header, Visual

Object Header and Video Object Layer Header)

  1. visual_object_sequence_end_code
  2. The header of the entry point function for an elementary stream

(Group_of_VideoObjectPlane() or the header of VideoObjectPlane(),

    video_plane_with_short_header(), MeshObject() or FaceObject())
 -  The video packet header (video_packet_header() excluding
    next_resync_marker())
 -  The header of gob_layer()
    See 6.2.1 "Start codes" of ISO/IEC 14496-2 [2][9][4] for the
    definition of the configuration information and the entry point
    functions.
 (1) Configuration information and Group_of_VideoObjectPlane() fields
 SHALL be placed at the beginning of the RTP payload (just after the
 RTP header) or just after the header of the syntactically upper layer
 function.
 (2) If one or more headers exist in the RTP payload, the RTP payload
 SHALL begin with the header of the syntactically highest function.
 Note: The visual_object_sequence_end_code is regarded as the lowest
 function.

Kikuchi, et al. Standards Track [Page 6] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 (3) A header SHALL NOT be split into a plurality of RTP packets.
 (4) Different VOPs SHOULD be fragmented into different RTP packets so
 that one RTP packet consists of the data bytes associated with a
 unique VOP time instance (that is indicated in the timestamp field in
 the RTP packet header), with the exception that multiple consecutive
 VOPs MAY be carried within one RTP packet in the decoding order if
 the size of the VOPs is small.
 Note: When multiple VOPs are carried in one RTP payload, the
 timestamp of the VOPs after the first one may be calculated by the
 decoder.  This operation is necessary only for RTP packets in which
 the marker bit equals to one and the beginning of RTP payload
 corresponds to a start code. (See timestamp and marker bit in section
 3.1.)
 (5) It is RECOMMENDED that a single video packet is sent as a single
 RTP packet.  The size of a video packet SHOULD be adjusted in such a
 way that the resulting RTP packet is not larger than the path-MTU.
 Note: Rule (5) does not apply when the video packet is disabled by
 the coder configuration (by setting resync_marker_disable in the VOL
 header to 1), or in coding tools where the video packet is not
 supported.  In this case, a VOP MAY be split at arbitrary byte-
 positions.
 The video packet starts with the VOP header or the video packet
 header, followed by motion_shape_texture(), and ends with
 next_resync_marker() or next_start_code().

3.3 Examples of packetized MPEG-4 Visual bitstream

 Figure 2 shows examples of RTP packets generated based on the
 criteria described in 3.2
 (a) is an example of the first RTP packet or the random access point
 of an MPEG-4 Visual bitstream containing the configuration
 information.  According to criterion (1), the Visual Object Sequence
 Header(VS header) is placed at the beginning of the RTP payload,
 preceding the Visual Object Header and the Video Object Layer
 Header(VO header, VOL header).  Since the fragmentation rule defined
 in 3.2 guarantees that the configuration information, starting with
 visual_object_sequence_start_code, is always placed at the beginning
 of the RTP payload, RTP receivers can detect the random access point
 by checking if the first 32-bit field of the RTP payload is
 visual_object_sequence_start_code.

Kikuchi, et al. Standards Track [Page 7] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 (b) is another example of the RTP packet containing the configuration
 information.  It differs from example (a) in that the RTP packet also
 contains a video packet in the VOP following the configuration
 information.  Since the length of the configuration information is
 relatively short (typically scores of bytes) and an RTP packet
 containing only the configuration information may thus increase the
 overhead, the configuration information and the immediately following
 GOV and/or (a part of) VOP can be packetized into a single RTP packet
 as in this example.
 (c) is an example of an RTP packet that contains
 Group_of_VideoObjectPlane(GOV).  Following criterion (1), the GOV is
 placed at the beginning of the RTP payload.  It would be a waste of
 RTP/IP header overhead to generate an RTP packet containing only a
 GOV whose length is 7 bytes.  Therefore, (a part of) the following
 VOP can be placed in the same RTP packet as shown in (c).
 (d) is an example of the case where one video packet is packetized
 into one RTP packet.  When the packet-loss rate of the underlying
 network is high, this kind of packetization is recommended.  Even
 when the RTP packet containing the VOP header is discarded by a
 packet loss, the other RTP packets can be decoded by using the
 HEC(Header Extension Code) information in the video packet header.
 No extra RTP header field is necessary.
 (e) is an example of the case where more than one video packet is
 packetized into one RTP packet.  This kind of packetization is
 effective to save the overhead of RTP/IP headers when the bit-rate of
 the underlying network is low.  However, it will decrease the
 packet-loss resiliency because multiple video packets are discarded
 by a single RTP packet loss.  The optimal number of video packets in
 an RTP packet and the length of the RTP packet can be determined
 considering the packet-loss rate and the bit-rate of the underlying
 network.
 (f) is an example of the case when the video packet is disabled by
 setting resync_marker_disable in the VOL header to 1.  In this case,
 a VOP may be split into a plurality of RTP packets at arbitrary
 byte-positions.  For example, it is possible to split a VOP into
 fixed-length packets.  This kind of coder configuration and RTP
 packet fragmentation may be used when the underlying network is
 guaranteed to be error-free.  On the other hand, it is not
 recommended to use it in error-prone environment since it provides
 only poor packet loss resiliency.
 Figure 3 shows examples of RTP packets prohibited by the criteria of
 3.2.

Kikuchi, et al. Standards Track [Page 8] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 Fragmentation of a header into multiple RTP packets, as in (a), will
 not only increase the overhead of RTP/IP headers but also decrease
 the error resiliency.  Therefore, it is prohibited by the criterion
 (3).
 When concatenating more than one video packets into an RTP packet,
 VOP header or video_packet_header() shall not be placed in the middle
 of the RTP payload.  The packetization as in (b) is not allowed by
 criterion (2) due to the aspect of the error resiliency.  Comparing
 this example with Figure 2(d), although two video packets are mapped
 onto two RTP packets in both cases, the packet-loss resiliency is not
 identical.  Namely, if the second RTP packet is lost, both video
 packets 1 and 2 are lost in the case of Figure 3(b) whereas only
 video packet 2 is lost in the case of Figure 2(d).
  +------+------+------+------+

(a) | RTP | VS | VO | VOL |

  |header|header|header|header|
  +------+------+------+------+
  +------+------+------+------+------------+

(b) | RTP | VS | VO | VOL |Video Packet|

  |header|header|header|header|            |
  +------+------+------+------+------------+
  +------+-----+------------------+

© | RTP | GOV |Video Object Plane|

  |header|     |                  |
  +------+-----+------------------+
  +------+------+------------+  +------+------+------------+

(d) | RTP | VOP |Video Packet| | RTP | VP |Video Packet|

  |header|header|    (1)     |  |header|header|    (2)     |
  +------+------+------------+  +------+------+------------+
  +------+------+------------+------+------------+------+------------+

(e) | RTP | VP |Video Packet| VP |Video Packet| VP |Video Packet|

  |header|header|     (1)    |header|    (2)     |header|    (3)     |
  +------+------+------------+------+------------+------+------------+
  +------+------+------------+  +------+------------+

(f) | RTP | VOP |VOP fragment| | RTP |VOP fragment|

  |header|header|    (1)     |  |header|    (2)     | ___
  +------+------+------------+  +------+------------+
   Figure 2 - Examples of RTP packetized MPEG-4 Visual bitstream

Kikuchi, et al. Standards Track [Page 9] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

  +------+-------------+  +------+------------+------------+

(a) | RTP |First half of| | RTP |Last half of|Video Packet|

  |header|  VP header  |  |header|  VP header |            |
  +------+-------------+  +------+------------+------------+
  +------+------+----------+  +------+---------+------+------------+

(b) | RTP | VOP |First half| | RTP |Last half| VP |Video Packet|

  |header|header| of VP(1) |  |header| of VP(1)|header|    (2)     |
  +------+------+----------+  +------+---------+------+------------+
 Figure 3 - Examples of prohibited RTP packetization for MPEG-4 Visual
 bitstream

4. RTP Packetization of MPEG-4 Audio bitstream

 This section specifies RTP packetization rules for MPEG-4 Audio
 bitstreams.  MPEG-4 Audio streams MUST be formatted by LATM (Low-
 overhead MPEG-4 Audio Transport Multiplex) tool [5], and the LATM-
 based streams are then mapped onto RTP packets as described the three
 sections below.

4.1 RTP Packet Format

 LATM-based streams consist of a sequence of audioMuxElements that
 include one or more audio frames.  A complete audioMuxElement or a
 part of one SHALL be mapped directly onto an RTP payload without any
 removal of audioMuxElement syntax elements (see Figure 4).  The first
 byte of each audioMuxElement SHALL be located at the first payload
 location in an RTP packet.

Kikuchi, et al. Standards Track [Page 10] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

V=2PX CC M PT sequence number

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

timestamp

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

synchronization source (SSRC) identifier

+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+

contributing source (CSRC) identifiers
….

+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+

: audioMuxElement (byte aligned) :Payload

:…OPTIONAL RTP padding

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 4 - An RTP packet for MPEG-4 Audio
 In order to decode the audioMuxElement, the following
 muxConfigPresent information is required to be indicated by an out-
 of-band means.  When SDP is utilized for this indication, MIME
 parameter "cpresent" corresponds to the muxConfigPresent information
 (see section 5.3).
 muxConfigPresent: If this value is set to 1 (in-band mode), the
 audioMuxElement SHALL include an indication bit "useSameStreamMux"
 and MAY include the configuration information for audio compression
 "StreamMuxConfig".  The useSameStreamMux bit indicates whether the
 StreamMuxConfig element in the previous frame is applied in the
 current frame.  If the useSameStreamMux bit indicates to use the
 StreamMuxConfig from the previous frame, but if the previous frame
 has been lost, the current frame may not be decodable.  Therefore, in
 case of in-band mode, the StreamMuxConfig element SHOULD be
 transmitted repeatedly depending on the network condition.  On the
 other hand, if muxConfigPresent is set to 0 (out-band mode), the
 StreamMuxConfig element is required to be transmitted by an out-of-
 band means.  In case of SDP, MIME parameter "config" is utilized (see
 section 5.3).

4.2 Use of RTP Header Fields for MPEG-4 Audio

 Payload Type (PT): The assignment of an RTP payload type for this new
 packet format is outside the scope of this document, and will not be
 specified here.  It is expected that the RTP profile for a particular
 class of applications will assign a payload type for this encoding,

Kikuchi, et al. Standards Track [Page 11] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 or if that is not done then a payload type in the dynamic range shall
 be chosen by means of an out of band signaling protocol (e.g., H.245,
 SIP, etc).  In the dynamic assignment of RTP payload types for
 scalable streams, a different value SHOULD be assigned to each layer.
 The assigned values SHOULD be in order of enhance layer dependency,
 where the base layer has the smallest value.
 Marker (M) bit: The marker bit indicates audioMuxElement boundaries.
 It is set to one to indicate that the RTP packet contains a complete
 audioMuxElement or the last fragment of an audioMuxElement.
 Timestamp: The timestamp indicates the sampling instance of the first
 audio frame contained in the RTP packet.  Timestamps are recommended
 to start at a random value for security reasons.
 Unless specified by an out-of-band means, the resolution of the
 timestamp is set to its default value of 90 kHz.
 Sequence Number: Incremented by one for each RTP packet sent,
 starting, for security reasons, with a random value.
 Other header fields are used as described in RFC 1889 [8].

4.3 Fragmentation of MPEG-4 Audio bitstream

 It is RECOMMENDED to put one audioMuxElement in each RTP packet.  If
 the size of an audioMuxElement can be kept small enough that the size
 of the RTP packet containing it does not exceed the size of the
 path-MTU, this will be no problem.  If it cannot, the audioMuxElement
 MAY be fragmented and spread across multiple packets.

5. MIME type registration for MPEG-4 Audio/Visual streams

 The following sections describe the MIME type registrations for
 MPEG-4 Audio/Visual streams.  MIME type registration and SDP usage
 for the MPEG-4 Visual stream are described in Sections 5.1 and 5.2,
 respectively, while MIME type registration and SDP usage for MPEG-4
 Audio stream are described in Sections 5.3 and 5.4, respectively.

5.1 MIME type registration for MPEG-4 Visual

 MIME media type name: video
 MIME subtype name: MP4V-ES
 Required parameters: none
 Optional parameters:

Kikuchi, et al. Standards Track [Page 12] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

    rate: This parameter is used only for RTP transport.  It indicates
    the resolution of the timestamp field in the RTP header.  If this
    parameter is not specified, its default value of 90000 (90kHz) is
    used.
    profile-level-id: A decimal representation of MPEG-4 Visual
    Profile and Level indication value (profile_and_level_indication)
    defined in Table G-1 of ISO/IEC 14496-2 [2][4].  This parameter
    MAY be used in the capability exchange or session setup procedure
    to indicate MPEG-4 Visual Profile and Level combination of which
    the MPEG-4 Visual codec is capable.  If this parameter is not
    specified by the procedure, its default value of 1 (Simple
    Profile/Level 1) is used.
    config: This parameter SHALL be used to indicate the configuration
    of the corresponding MPEG-4 Visual bitstream.  It SHALL NOT be
    used to indicate the codec capability in the capability exchange
    procedure.  It is a hexadecimal representation of an octet string
    that expresses the MPEG-4 Visual configuration information, as
    defined in subclause 6.2.1 Start codes of ISO/IEC14496-2
    [2][4][9].  The configuration information is mapped onto the octet
    string in an MSB-first basis.  The first bit of the configuration
    information SHALL be located at the MSB of the first octet.  The
    configuration information indicated by this parameter SHALL be the
    same as the configuration information in the corresponding MPEG-4
    Visual stream, except for first_half_vbv_occupancy and
    latter_half_vbv_occupancy, if exist, which may vary in the
    repeated configuration information inside an MPEG-4 Visual stream
    (See 6.2.1 Start codes of ISO/IEC14496-2).
    Example usages for these parameters are:
  1. MPEG-4 Visual Simple Profile/Level 1:

Content-type: video/mp4v-es; profile-level-id=1

  1. MPEG-4 Visual Core Profile/Level 2:

Content-type: video/mp4v-es; profile-level-id=34

  1. MPEG-4 Visual Advanced Real Time Simple Profile/Level 1:

Content-type: video/mp4v-es; profile-level-id=145

 Published specification:
    The specifications for MPEG-4 Visual streams are presented in
    ISO/IEC 14469-2 [2][4][9].  The RTP payload format is described in
    RFC 3016.

Kikuchi, et al. Standards Track [Page 13] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 Encoding considerations:
    Video bitstreams MUST be generated according to MPEG-4 Visual
    specifications (ISO/IEC 14496-2).  A video bitstream is binary
    data and MUST be encoded for non-binary transport (for Email, the
    Base64 encoding is sufficient).  This type is also defined for
    transfer via RTP.  The RTP packets MUST be packetized according to
    the MPEG-4 Visual RTP payload format defined in RFC 3016.
 Security considerations:
    See section 6 of RFC 3016.
 Interoperability considerations:
    MPEG-4 Visual provides a large and rich set of tools for the
    coding of visual objects.  For effective implementation of the
    standard, subsets of the MPEG-4 Visual tool sets have been
    provided for use in specific applications.  These subsets, called
    'Profiles', limit the size of the tool set a decoder is required
    to implement.  In order to restrict computational complexity, one
    or more Levels are set for each Profile.  A Profile@Level
    combination allows:
    o a codec builder to implement only the subset of the standard he
    needs, while maintaining interworking with other MPEG-4 devices
    included in the same combination, and
    o checking whether MPEG-4 devices comply with the standard ('
    conformance testing').
    The visual stream SHALL be compliant with the MPEG-4 Visual
    Profile@Level specified by the parameter "profile-level-id".
    Interoperability between a sender and a receiver may be achieved
    by specifying the parameter "profile-level-id" in MIME content, or
    by arranging in the capability exchange/announcement procedure to
    set this parameter mutually to the same value.
 Applications which use this media type:
    Audio and visual streaming and conferencing tools, Internet
    messaging and Email applications.
 Additional information: none
 Person & email address to contact for further information:
    The authors of RFC 3016.  (See section 8.)
 Intended usage: COMMON
 Author/Change controller:
    The authors of RFC 3016.  (See section 8.)

Kikuchi, et al. Standards Track [Page 14] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

5.2 SDP usage of MPEG-4 Visual

 The MIME media type video/MP4V-ES string is mapped to fields in the
 Session Description Protocol (SDP), RFC 2327, as follows:
 o  The MIME type (video) goes in SDP "m=" as the media name.
 o  The MIME subtype (MP4V-ES) goes in SDP "a=rtpmap" as the encoding
    name.
 o  The optional parameter "rate" goes in "a=rtpmap" as the clock
    rate.
 o  The optional parameter "profile-level-id" and "config" go in the
    "a=fmtp" line to indicate the coder capability and configuration,
    respectively.  These parameters are expressed as a MIME media type
    string, in the form of as a semicolon separated list of
    parameter=value pairs.
 The following are some examples of media representation in SDP:

Simple Profile/Level 1, rate=90000(90kHz), "profile-level-id" and "config" are present in "a=fmtp" line:

m=video 49170/2 RTP/AVP 98
a=rtpmap:98 MP4V-ES/90000
a=fmtp:98 profile-level-id=1;config=000001B001000001B509000001000000012
   0008440FA282C2090A21F

Core Profile/Level 2, rate=90000(90kHz), "profile-level-id" is present in "a=fmtp" line:

m=video 49170/2 RTP/AVP 98
a=rtpmap:98 MP4V-ES/90000
a=fmtp:98 profile-level-id=34

Advance Real Time Simple Profile/Level 1, rate=90000(90kHz), "profile-level-id" is present in "a=fmtp" line:

m=video 49170/2 RTP/AVP 98
a=rtpmap:98 MP4V-ES/90000
a=fmtp:98 profile-level-id=145

5.3 MIME type registration of MPEG-4 Audio

 MIME media type name: audio
 MIME subtype name: MP4A-LATM

Kikuchi, et al. Standards Track [Page 15] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 Required parameters:
    rate: the rate parameter indicates the RTP time stamp clock rate.
    The default value is 90000.  Other rates MAY be specified only if
    they are set to the same value as the audio sampling rate (number
    of samples per second).
 Optional parameters:
    profile-level-id: a decimal representation of MPEG-4 Audio Profile
    Level indication value defined in ISO/IEC 14496-1 ([6] and its
    amendments).  This parameter indicates which MPEG-4 Audio tool
    subsets the decoder is capable of using.  If this parameter is not
    specified in the capability exchange or session setup procedure,
    its default value of 30 (Natural Audio Profile/Level 1) is used.
    object: a decimal representation of the MPEG-4 Audio Object Type
    value defined in ISO/IEC 14496-3 [5].  This parameter specifies
    the tool to be used by the coder.  It CAN be used to limit the
    capability within the specified "profile-level-id".
    bitrate: the data rate for the audio bit stream.
    cpresent: a boolean parameter indicates whether audio payload
    configuration data has been multiplexed into an RTP payload (see
    section 4.1).  A 0 indicates the configuration data has not been
    multiplexed into an RTP payload, a 1 indicates that it has.  The
    default if the parameter is omitted is 1.
    config: a hexadecimal representation of an octet string that
    expresses the audio payload configuration data "StreamMuxConfig",
    as defined in ISO/IEC 14496-3 [5] (see section 4.1).
    Configuration data is mapped onto the octet string in an MSB-first
    basis.  The first bit of the configuration data SHALL be located
    at the MSB of the first octet.  In the last octet, zero-padding
    bits, if necessary, SHALL follow the configuration data.
    ptime: RECOMMENDED duration of each packet in milliseconds.
 Published specification:
    Payload format specifications are described in this document.
    Encoding specifications are provided in ISO/IEC 14496-3 [3][5].
 Encoding considerations:
    This type is only defined for transfer via RTP.
 Security considerations:
    See Section 6 of RFC 3016.

Kikuchi, et al. Standards Track [Page 16] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 Interoperability considerations:
    MPEG-4 Audio provides a large and rich set of tools for the coding
    of audio objects.  For effective implementation of the standard,
    subsets of the MPEG-4 Audio tool sets similar to those used in
    MPEG-4 Visual have been provided (see section 5.1).
    The audio stream SHALL be compliant with the MPEG-4 Audio
    Profile@Level specified by the parameter "profile-level-id".
    Interoperability between a sender and a receiver may be achieved
    by specifying the parameter "profile-level-id" in MIME content, or
    by arranging in the capability exchange procedure to set this
    parameter mutually to the same value.  Furthermore, the "object"
    parameter can be used to limit the capability within the specified
    Profile@Level in capability exchange.
 Applications which use this media type:
    Audio and video streaming and conferencing tools.
 Additional information: none
 Personal & email address to contact for further information:
    See Section 8 of RFC 3016.
 Intended usage: COMMON
 Author/Change controller:
    See Section 8 of RFC 3016.

5.4 SDP usage of MPEG-4 Audio

 The MIME media type audio/MP4A-LATM string is mapped to fields in the
 Session Description Protocol (SDP), RFC 2327, as follows:
 o  The MIME type (audio) goes in SDP "m=" as the media name.
 o  The MIME subtype (MP4A-LATM) goes in SDP "a=rtpmap" as the
    encoding name.
 o  The required parameter "rate" goes in "a=rtpmap" as the clock
    rate.
 o  The optional parameter "ptime" goes in SDP "a=ptime" attribute.
 o  The optional parameter "profile-level-id" goes in the "a=fmtp"
    line to indicate the coder capability.  The "object" parameter
    goes in the "a=fmtp" attribute.  The payload-format-specific
    parameters

Kikuchi, et al. Standards Track [Page 17] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

    "bitrate", "cpresent" and "config" go in the "a=fmtp" line.  These
    parameters are expressed as a MIME media type string, in the form
    of as a semicolon separated list of parameter=value pairs.
 The following are some examples of the media representation in SDP:

For 6 kb/s CELP bitstreams (with an audio sampling rate of 8 kHz),

m=audio 49230 RTP/AVP 96
a=rtpmap:96 MP4A-LATM/8000
a=fmtp:96 profile-level-id=9;object=8;cpresent=0;config=9128B1071070
a=ptime:20
 For 64 kb/s AAC LC stereo bitstreams (with an audio sampling rate of
 24 kHz),
    m=audio 49230 RTP/AVP 96
    a=rtpmap:96 MP4A-LATM/24000
    a=fmtp:96 profile-level-id=1; bitrate=64000; cpresent=0;
    config=9122620000
 In the above two examples, audio configuration data is not
 multiplexed into the RTP payload and is described only in SDP.
 Furthermore, the "clock rate" is set to the audio sampling rate.
 If the clock rate has been set to its default value and it is
 necessary to obtain the audio sampling rate, this can be done by
 parsing the "config" parameter (see the following example).
    m=audio 49230 RTP/AVP 96
    a=rtpmap:96 MP4A-LATM/90000
    a=fmtp:96 object=8; cpresent=0; config=9128B1071070
 The following example shows that the audio configuration data appears
 in the RTP payload.
    m=audio 49230 RTP/AVP 96
    a=rtpmap:96 MP4A-LATM/90000
    a=fmtp:96 object=2; cpresent=1

6. Security Considerations

 RTP packets using the payload format defined in this specification
 are subject to the security considerations discussed in the RTP
 specification [8].  This implies that confidentiality of the media
 streams is achieved by encryption.  Because the data compression used
 with this payload format is applied end-to-end, encryption may be
 performed on the compressed data so there is no conflict between the
 two operations.

Kikuchi, et al. Standards Track [Page 18] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

 The complete MPEG-4 system allows for transport of a wide range of
 content, including Java applets (MPEG-J) and scripts.  Since this
 payload format is restricted to audio and video streams, it is not
 possible to transport such active content in this format.

7. References

 1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
    9, RFC 2026, October 1996.
 2  ISO/IEC 14496-2:1999, "Information technology - Coding of audio-
    visual objects - Part2: Visual".
 3  ISO/IEC 14496-3:1999, "Information technology - Coding of audio-
    visual objects - Part3: Audio".
 4  ISO/IEC 14496-2:1999/Amd.1:2000, "Information technology - Coding
    of audio-visual objects - Part 2: Visual, Amendment 1: Visual
    extensions".
 5  ISO/IEC 14496-3:1999/Amd.1:2000, "Information technology - Coding
    of audio-visual objects - Part3: Audio, Amendment 1: Audio
    extensions".
 6  ISO/IEC 14496-1:1999, "Information technology - Coding of audio-
    visual objects - Part1: Systems".
 7  Bradner, S., "Key words for use in RFCs to Indicate Requirement
    Levels", BCP 14, RFC 2119, March 1997.
 8  Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson "RTP: A
    Transport Protocol for Real Time Applications", RFC 1889, January
    1996.
 9  ISO/IEC 14496-2:1999/Cor.1:2000, "Information technology - Coding
    of audio-visual objects - Part2: Visual, Technical corrigendum 1".

Kikuchi, et al. Standards Track [Page 19] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

8. Authors' Addresses

 Yoshihiro Kikuchi
 Toshiba corporation
 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki, 212-8582, Japan
 EMail: yoshihiro.kikuchi@toshiba.co.jp
 Yoshinori Matsui
 Matsushita Electric Industrial Co., LTD.
 1006, Kadoma, Kadoma-shi, Osaka, Japan
 EMail: matsui@drl.mei.co.jp
 Toshiyuki Nomura
 NEC Corporation
 4-1-1,Miyazaki,Miyamae-ku,Kawasaki,JAPAN
 EMail: t-nomura@ccm.cl.nec.co.jp
 Shigeru Fukunaga
 Oki Electric Industry Co., Ltd.
 1-2-27 Shiromi, Chuo-ku, Osaka 540-6025 Japan.
 EMail: fukunaga444@oki.co.jp
 Hideaki Kimata
 Nippon Telegraph and Telephone Corporation
 1-1, Hikari-no-oka, Yokosuka-shi, Kanagawa, Japan
 EMail: kimata@nttvdt.hil.ntt.co.jp

Kikuchi, et al. Standards Track [Page 20] RFC 3016 RTP Payload Format for MPEG-4 Audio/Visual November 2000

9. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Kikuchi, et al. Standards Track [Page 21]

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