[asterisk-users] Why doesn't Asterisk try to prevent transcoding

jg webaccounts at jgoettgens.de
Sun Dec 15 08:32:21 CST 2013

> You are correct. Your idea of the prioritize_matching_codecs option is what I am looking for. 
> Yes Asterisk can transcode, but why transcode when you don't need to. If the phone is 
> advertising both formats it should support them. If the phone only supports local MOH in one 
> format then the phone should only advertise that format.
But things may change during a call or you are stuck with whatever the phone uses for its MOH, 
which only some people use.
> If Answer and Playback are called first then the format would have already been sent back in 
> the 200 OK and Asterisk would transcode when Dial is called. If Dial is called first, change 
> the format for the 200 OK and use it for the rest of the call. I haven't looked into what 
> happens with transfers.
A lot. You need to consider SIP INVITEs as well as Asterisk features (DTMF signals). Some time 
ago I had a problem with a codec mismatch when only Local channels (Asterisk features uses them) 
appeared to be involved.
> The idea comes from the following setup. I have 450 users on a FreePBX / Asterisk server with 
> a Sangoma transcoding card. However I am limited in the number of sessions. I also have a 
> number of smaller 10-50 user deployments without transcoding cards.
Is it possible to let the Sangoma card work only on the most demanding codecs? This requires 
some analysis to estimate the benefits. Another question is whether the user phones are 
provisioned or not. If provisioned, then you are the maker of rules.

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