[AVT] Vorbis RTP issues list for Vienna

[philkerr@elec.gla.ac.uk]

Dear all,

Last month (11th June) an -02 update to draft-kerr-avt-vorbis-rtp was announced
on the AVT list and a slot in Vienna has been booked for discussion.

The draft details the RTP delivery of Vorbis audio, SDP values and delivery of
the decoders static probability model, 'codebooks'.  Examples of Vorbis frame
packing and fragmented packet handling are also covered.

Open issues:

Congestion control.  Under development is a mechanism for dynamic bitrate
reduction called 'bitrate peeling'.  When this feature becomes available it will
impact on how congestion is dealt with and a mechanism allowing its use within a
 multicast environment needs to be explored.

Codebook delivery.  There are two mechanisms outlined for the delivery of the
codebooks, SDP and RTCP.  The codebooks may change mid-stream (at the boundary
between two tracks) as well as being static for the session lifetime.  As the
codebooks are needed for the successful decoding of the Vorbis stream a reliable
mechanism to handle their delivery of mid-session codebook changes should be
investigated (TCP over RTP?) in preference to using RTCP messages.

Path MTU.  There is a mechanism for splitting large Vorbis frames across
multiple RTP packets but a reliable mechanism for path-MTU discovery needs to be
outlined to prevent packet fragmentation not dealt with by the above.

I've also requested WG status for the I-D.


Comments and feedback welcomed.

Regards

Phil



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