[vorbis] Rgenerating headers

[Peter Maersk-Moller]

Hi

So far when I have streamed Vorbis, the headers (the 3 first
frames/packets) was not included in the stream, but communicated
out of band typically in an SDP file as unparsed A-lines.

Rethinking that concept, I'm wondering if it is really necessary
to do it that way. Isn't it possible in a platform independent
way to regenerate useable headers on the client side using
just the following parameters

   Vorbis version
   number of channels
   sample rate
   max bit rate
   nominel bit rate
   minimum bit rate

So instead of using several thousand bytes, adding somthing
to the SDP file like

   a=vorbis_header: "0,2,44100,128000,128000,-1"

would be sufficient to regenerate the headers ignoring the loss
of comments from the comment header.

If comments were really needed, they could also be communicated
out of band in the SDP file something like

   a=vorbis_comment: "Copyright" "Some One"
   a=vorbis_comment: "Date" "Some date"

or

   a=vorbis_comment_url: "http://some_server/some_path/some_file"

but that's rather dangerous for multicast if the client auto
download the URL.

So, back to my question - is there any reason why you shouldn't
be able to completely regenerate the header packets/frames
from what I have outlined ?

--PMM

-----------------------------------------------------------
Peter Maersk-Moller
-----------------------------------------------------------
Ogg/Vorbis support for MPEG4IP and YUV12, XviD, AVI and MP4
for libmpeg2. See http://www.maersk-moller.net/projects/
-----------------------------------------------------------

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