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RTP Payload Format for MPEG-4 Audio/Visual Streams
draft-ietf-avt-rtp-mpeg4-es-05

The information below is for an old version of the document that is already published as an RFC.
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This is an older version of an Internet-Draft that was ultimately published as RFC 3016.
Authors Yoshinori Matsui , Hideaki Kimata , Yoshihiro Kikuchi , Shigeru Fukunaga , Toshiyuki Nomura
Last updated 2013-03-02 (Latest revision 2000-10-12)
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draft-ietf-avt-rtp-mpeg4-es-05
Internet Engineering Task Force                 Yoshihiro Kikuchi - Toshiba
Internet Draft                                       Toshiyuki Nomura - NEC
Document: draft-ietf-avt-rtp-mpeg4-es-05.txt         Shigeru Fukunaga - Oki
                                              Yoshinori Matsui - Matsushita
                                                       Hideaki Kimata - NTT
                                                           October 11, 2000

             RTP payload format for MPEG-4 Audio/Visual streams

Status of this Memo

   This document is an Internet-Draft and is in full conformance with all
      provisions of Section 10 of RFC2026 [1].

   Internet-Drafts are working documents of the Internet Engineering Task
   Force (IETF), its areas, and its working groups. Note that other groups
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   http://www.ietf.org/ietf/1id-abstracts.txt
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                                   Abstract

   This document describes 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
   MIME type registrations and the use of SDP.

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RTP payload format for MPEG-4 Audio/Visual streams      September 2000

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 functionality and thus require no such
   functionality from MPEG-4 Systems. H.323 terminals are an example of such
   a 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.

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RTP payload format for MPEG-4 Audio/Visual streams      September 2000

   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 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;
   - Carrying configuration information with audio data,
   - Concatenation of multiple audio frames in one audio stream,
   - Multiplexing multiple objects (programs),
   - 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 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).

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   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).

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RTP payload format for MPEG-4 Audio/Visual streams      September 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=2|P|X|  CC   |M|     PT      |       sequence number         | RTP
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           timestamp                           | Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           synchronization source (SSRC) identifier            |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |            contributing source (CSRC) identifiers             |
   |                             ....                              |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                                                               | RTP
   |       MPEG-4 Visual stream (byte aligned)                     | Payload
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...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 1.

   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.
   - 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 the VOPs are derived

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     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:
   - Configuration information (Visual Object Sequence Header, Visual Object
     Header and Video Object Layer Header)
   - visual_object_sequence_end_code
   - 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.

   (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

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RTP payload format for MPEG-4 Audio/Visual streams      September 2000

   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.

   (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

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   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.

   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).

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RTP payload format for MPEG-4 Audio/Visual streams      September 2000

       +------+------+------+------+
   (a) | RTP  |  VS  |  VO  | VOL  |
       |header|header|header|header|
       +------+------+------+------+

       +------+------+------+------+------------+
   (b) | RTP  |  VS  |  VO  | VOL  |Video Packet|
       |header|header|header|header|            |
       +------+------+------+------+------------+

       +------+-----+------------------+
   (c) | 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

       +------+-------------+  +------+------------+------------+
   (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

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RTP payload format for MPEG-4 Audio/Visual streams      September 2000

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.

   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=2|P|X|  CC   |M|     PT      |       sequence number         |RTP
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           timestamp                           |Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           synchronization source (SSRC) identifier            |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |            contributing source (CSRC) identifiers             |
   |                             ....                              |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                                                               |RTP
   :                 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

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   (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, 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.

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   (In the following sections, the RFC number "XXXX" represents the RFC
   number, which should be assigned for this document.)

5.1 MIME type registration for MPEG-4 Visual

   MIME media type name: video

   MIME subtype name: MP4V-ES

   Required parameters: none

   Optional parameters:
     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
     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:
       - MPEG-4 Visual Simple Profile/Level 1:
          Content-type: video/mp4v-es; profile-level-id=1

       - MPEG-4 Visual Core Profile/Level 2:
          Content-type: video/mp4v-es; profile-level-id=34

       - MPEG-4 Visual Advanced Real Time Simple Profile/Level 1:
          Content-type: video/mp4v-es; profile-level-id=145

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RTP payload format for MPEG-4 Audio/Visual streams      September 2000

   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 RFCXXXX.

   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 RFCXXXX.

   Security considerations:
     See section 6 of RFCXXXX.

   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 RFCXXXX. (See section 8)

   Intended usage: COMMON

   Author/Change controller:

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     The authors of RFCXXXX. (See section 8)

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=25(25Hz), "profile-level-
   id" is present in "a=fmtp" line:
     m=video 49170/2 RTP/AVP 98
     a=rtpmap:98 MP4V-ES/25
     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

   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

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     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 [10]. 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: this parameter indicates whether audio payload configuration
     data has been multiplexed into an RTP payload (see section 4.1). If
     not specified, the default value 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 RFCXXXX.

   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

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RTP payload format for MPEG-4 Audio/Visual streams      September 2000

     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 RFCXXXX.

   Intended usage: COMMON

   Author/Change controller:
     See Section 8 of RFCXXXX.

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 "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),

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RTP payload format for MPEG-4 Audio/Visual streams      September 2000

     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.

   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", December 1999.

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RTP payload format for MPEG-4 Audio/Visual streams      September 2000

   3 ISO/IEC 14496-3:1999, "Information technology - Coding of audio-visual
      objects - Part3: Audio", December 1999.

   4 ISO/IEC 14496-2:1999/FDAM1:2000, December 1999.

   5 ISO/IEC 14496-3:1999/FDAM1:2000, December 1999.

   6 ISO/IEC 14496-1:1999, "Information technology - Coding of audio-visual
      objects - Part1: Systems", December 1999.

   7  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997

   8 H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson "RTP: A Transport
      Protocol for Real Time Applications",  RFC 1889, Internet Engineering
      Task Force, January 1996.

   9  ISO/IEC 14496-2:1999/COR1:2000, "Information technology - Coding of
      audio-visual objects - Part2: Visual, Technical corrigendum 1", August
      2000.

   10 ISO/IEC 14496-1:1999/FDAM1:2000, December 1999.

8. Author's 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

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