RFC 2343 (rfc2343) - Page 2 of 8

RTP Payload Format for Bundled MPEG

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