RTP Payload Format for Bundled MPEG
RFC 2343
| Document | Type |
RFC - Experimental
(May 1998; No errata)
Was draft-civanlar-bmpeg (avt WG)
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|---|---|---|---|
| Last updated | 2013-03-02 | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 2343 (Experimental) | |
| Consensus Boilerplate | Unknown | ||
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Network Working Group M. Civanlar
Request for Comments: 2343 G. Cash
Category: Experimental B. Haskell
AT&T Labs-Research
May 1998
RTP Payload Format for Bundled MPEG
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. This memo does not specify an Internet standard of any
kind. Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
This document describes a payload type for bundled, MPEG-2 encoded
video and audio data that may be used with RTP, version 2. Bundling
has some advantages for this payload type particularly when it is
used for video-on-demand applications. This payload type may be used
when its advantages are important enough to sacrifice the modularity
of having separate audio and video streams.
1. Introduction
This document describes a bundled packetization scheme for MPEG-2
encoded audio and video streams using the Real-time Transport
Protocol (RTP), version 2 [1].
The MPEG-2 International standard consists of three layers: audio,
video and systems [2]. The audio and the video layers define the
syntax and semantics of the corresponding "elementary streams." The
systems layer supports synchronization and interleaving of multiple
compressed streams, buffer initialization and management, and time
identification. RFC 2250 [3] describes packetization techniques to
transport individual audio and video elementary streams as well as
the transport stream, which is defined at the system layer, using the
RTP.
Civanlar, et. al. Experimental [Page 1]
RFC 2343 RTP Payload Format for Bundled MPEG May 1998
The bundled packetization scheme is needed because it has several
advantages over other schemes for some important applications
including video-on-demand (VOD) where, audio and video are always
used together. Its advantages over independent packetization of
audio and video are:
1. Uses a single port per "program" (i.e. bundled A/V). This may
increase the number of streams that can be served e.g., from a VOD
server. Also, it eliminates the performance hit when two ports are
used for the separate audio and video streams on the client side.
2. Provides implicit synchronization of audio and video. This is
particularly convenient when the A/V data is stored in an
interleaved format at the server.
3. Reduces the header overhead. Since using large packets increases
the effects of losses and delay, audio only packets need to be
smaller increasing the overhead. An A/V bundled format can provide
about 1% overall overhead reduction. Considering the high bitrates
used for MPEG-2 encoded material, e.g. 4 Mbps, the number of bits
saved, e.g. 40 Kbps, may provide noticeable audio or video quality
improvement.
4. May reduce overall receiver buffer size. Audio and video streams
may experience different delays when transmitted separately. The
receiver buffers need to be designed for the longest of these
delays. For example, let's assume that using two buffers, each with
a size B, is sufficient with probability P when each stream is
transmitted individually. The probability that the same buffer size
will be sufficient when both streams need to be received is P times
the conditional probability of B being sufficient for the second
stream given that it was sufficient for the first one. This
conditional probability is, generally, less than one requiring use
of a larger buffer size to achieve the same probability level.
5. May help with the control of the overall bandwidth used by an
A/V program.
And, the advantages over packetization of the transport layer streams
are:
1. Reduced overhead. It does not contain systems layer information
which is redundant for the RTP (essentially they address similar
issues).
Civanlar, et. al. Experimental [Page 2]
RFC 2343 RTP Payload Format for Bundled MPEG May 1998
2. Easier error recovery. Because of the structured packetization
consistent with the application layer framing (ALF) principle, loss
concealment and error recovery can be made simpler and more
effective.
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