Re: [GnomeMeeting-devel-list] Speex

[Damien Sandras <dsandras seconix com>]

Le dimanche 12 mars 2006 à 12:58 +0100, Olaf Conradi a écrit :
> Hmm, ok. I read the Speex RFC draft as: if the the offerer does not
> specify a mode, assume it supports all modes. Ofcourse this is not
> explicitly stated. Indeed, it does not accurately specify what to do.
> 

It would be more correct to assume it doesn't support all modes.

> After reading the iLBC RFC [1], I notice it assumes if unspecified
> default mode is iLBC mode 30. But if offerer and answerer differ in
> mode, the *lower bandwidth* one is preferred. So offer 30 (or not
> specified) and answer mode 20 will result in mode 30 being used, which
> happens to be the default.
> 

Yes, that is why it was chosen as "default".
You have the same kind of reasoning with H.261 and some other codecs.
The reason is that many endpoints do not support modes, so the "default"
should always be the chosen mode except when we are sure that both
endpoints support another mode than the default.


> Applying the "prefer lowest bandwidth mode" between offerer and
> answerer to Speex will make my example from above (offerer requests -
> unspecified - mode 3, answerer responds with 5) invalid and the lower
> mode 3 shall be used.
> 
> But Speex supports 6 modes. So if I responded with mode 2, then mode 2
> should be used.
> 

Then it won't work with endpoints that do not support modes.

> Cheers,
> Olaf
> 
> [1] http://www.ietf.org/rfc/rfc3952.txt
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