Posted: Wed Oct 25, 2006 6:04 am Post subject: [Iaxclient-devel] [Asterisk-video] Re: Re: Video codec negot
On Oct 25, 2006, at 10:44 AM, Mihai Balea wrote:
Quote:
The main reason for this is that RTP packets carry media type
information in the header.
In IAX, we'll probably have to use a full frame for this (mini frames
have only minimal information in their 4-byte headers).
It would be doable, but it will probably require some changes in the
way codecs are negotiated.
Something to think about....
That's the way IAX works now for audio -- a full frame is sent
explicitly if the codec changes..
From iax.c in libiax2, for example:
if (((fts & 0xFFFF0000L) == (lastsent & 0xFFFF0000L))
/* High two bits are the same on timestamp, or
sending on a trunk */ &&
(f->frametype == AST_FRAME_VOICE)
/* is a voice frame */ &&
(f->subclass == pvt->svoiceformat)
/* is the same type */ ) {
/* Force immediate rather than delayed
transmission */
now = 1;
/* Mark that mini-style frame is appropriate */
sendmini = 1;
}
sendmini is only set on all these conditions, one of which is that
the format is the same.
-SteveK
Quote:
Mihai
On Oct 25, 2006, at 4:26 AM, Olle E Johansson wrote:
> The interesting part in all of this is that Asterisk is able to
> negotiate a SIP call with
> multiple codecs, and change codec mid-call without re-negotation.
> The RTP stack
> will just notify that we changed codec and the translators seems to
> be in place
> somehow. I have no idea on the inner workings, but it works.
>
> In that case, no re-invite is needed, since it was already
> negotiated.
>
> /O
>
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