Network Working Group Y. Kikuchi
Request for Comments: 3016 Toshiba
Category: Standards Track T. Nomura
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 (C) The Internet Society (2000). All Rights Reserved.
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).
The RTP payload formats described in this document specify how MPEG-4
Audio  and MPEG-4 Visual streams  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 . 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. . 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