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

[Colin Perkins <csp at csperkins.org>]

On Thursday 06 May 2004 17:13, Dave Singer wrote:
> >  > >- 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?

I wouldn't go into too much detail, but certainly mentioning these points 
is worthwhile.

-- 
Colin Perkins
http://csperkins.org/

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