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Re: [AVT] I-D ACTION:draft-ietf-avt-rtp-h264-05.txt



 > >- In the encoding considerations for the MIME type, may wish to note
 > that file formats are defined elsewhere?

 The problem here is that all file formats are still in their
 specification phase -- we can't reference them (yet).  And what good
 would a simple "elsewhere" do?
Questions about the lack of a file format have been raised during IESG
review of other RTP payload formats. Noting that the formats are being
defined elsewhere will avoid the question later.
Then perhaps it is appropriate to say a little more.

MPEG has defined the storage of AVC/H.264 content in ISO-family files, and that specification is published. It's not expected to be used standalone, of course, as video is rarely found standalone (usually with audio). So this does define the storage of AVC in MP4, 3GP, 3GP2 and so on. RTP packetization of this format shouldn't be excessively problematic, as it stores whole NAL Units in the same form as the RTP payload, and hint tracks can also be used if appropriate to pre-compute packetization.

The packing of AVC/H.264 into MPEG-2 transport streams is also defined, so it is also possible to encounter MPEG-2 transport-streams-frozen-on-disk which contain H.264. The RTP packetization of those would involve changing the NAL Units from start-code to length-fields, and I expect other operations.

Would text like this help?
--
David Singer
Apple Computer/QuickTime

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