[asterisk-dev] Fwd: [Iaxclient-devel] Video codec negotiation in IAX

[Mihai Balea]

Hello all,

I am working on the Iaxclient project (http://sourceforge.net/ 
projects/iaxclient).  We are trying to add video support to our code,  
but we have some problems with video codec negotiation with Asterisk.

Please see message included below.  I've already sent this to  
iaxclient-devel and asterisk-video lists, but I figured that the  
general Asterisk development community might have some insightful  
opinions...

Thanks in advance,
Mihai

Begin forwarded message:

> From: Mihai Balea <mihai at hates.ms>
> Date: October 23, 2006 11:45:13 AM EDT
> To: Iax Developer List <iaxclient-devel at lists.sourceforge.net>
> Cc: asterisk-video at lists.digium.com
> Subject: [Iaxclient-devel] Video codec negotiation in IAX
>
> Hello all,
>
> As you may already know, I am working on adding video support to
> iaxclient.
>
> It appears however that IAX's support for video codec negotiation is
> lacking.  I am no IAX expert, but from what I can see, there are to
> ways of doing codec negotiation in IAX:
> - use the FORMAT and CAPABILITY IEs.  This allows you to specify one
> preferred codec and a list of acceptable codecs. This is the way
> iaxclient does codec negotiation at this time.
> - use the CODEC PREFS IE.  This allows you to specify a list of
> acceptable codecs, in order of preference.
>
> The problem with video is that you need to negotiate two codecs at
> the same time (one for video and one for audio). Unfortunately, none
> of the above mentioned methods are suitable for this.  The way I see
> it, there are several ways of addressing this:
> 1. use a VIDEO FORMAT IE, in addition to FORMAT and CAPABILITY.  The
> CAPABILITY IE will contain acceptable video codecs as well as audio.
> 2. use a VIDEO CODEC PREFS IE in addition to the current CODEC PREFS
> IE.  This will more flexible since it allows for video codec
> preference order.
> 3. use the current FORMAT and CAPABILITY and change the semantics of
> FORMAT to allow a video codec as well as an audio codec. This might
> be easiest to implement.
>
> As a long term solution, I'm inclined to go with #2 since it provides
> the maximum amount of flexibility.  However I would like to hear any
> suggestions you might have regarding this issue...
>
> Thanks in advance,
> Mihai
>
>
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