[theora] Theora over RTP - update

Silvia Pfeiffer silviapfeiffer1 at gmail.com
Tue Feb 9 13:41:18 PST 2010

It would be great if you could send us a patch to the draft RFC with
these changes. That would definitely help make interoperable
implementations of Theora streaming over RTP.


On Wed, Feb 10, 2010 at 4:06 AM, Gisle Sælensminde <gisle at snirklasjon.no> wrote:
> I have now studied the source of Ekiga to see how that wraps the Theora
> payload in RTP, and how packets are encoded and decoded there, since it
> seems to do aproximatly the same as I try to do. I did the following
> observations:
> - The Theora/RTP draft specifies that the theora header packet and
> theora tables should be merged into one RTP packet, but there were no
> explanation about how that combined RTP packet should be decoded. The
> reason that is possible, is that the Theora header packet has a fixed
> size of 42 bytes, so to find the tables, you just use an offset of 42
> into the header packet. That is not explained anywhere in the draft.
> - The Theora/RTP draft define additional headers after the RTP headers,
> but before the Theora payload. This included an id (24bits),
> fragment_type, and number of Theora packets in the RTP packet. In Ekiga
> this is always 0xdedede.  Since they always use the same parameter set,
> this is probably OK.
> - Why is the comments header called "legacy comments" in the draft?
> - The fields of the ogg_packet structure (like width, height, etc) must
> be manually filled by the RTP decoder, before sending it into the theora
> decoder.
> I think this should be sufficient for me to be able to implementing
> theora support. Thank you all for pointing me in the right direction.
> Other than that, the draft specifies clearly how packets should be
> formated. Some places maybe even in too much detail (No need to explain
> the RTP header fields, they can be found in the RTP standard).
> -Gisle
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