RFC 2343 (rfc2343) - Page 2 of 8
RTP Payload Format for Bundled MPEG
Alternative Format: Original Text Document
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