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

Ryan Wagoner rswagoner at gmail.com
Sun Dec 15 10:36:53 CST 2013

On Sun, Dec 15, 2013 at 9:32 AM, jg <webaccounts at jgoettgens.de> wrote:

> 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.
Most users have both a desk Polycom phone and a soft phone on their mobile
device or laptop. I don't have control over how the soft phones are
provisioned on mobile devices. I've found a workaround that prevents
transcoding for outbound calls.

remote phone

local phone


In FreePBX extensions_custom.conf I've added the following. This tries to
force the outbound channel to match the inbound channel's format.

exten =>

Remote to local g729 pass through
Local to remote g729 transcoding
Local to trunk ulaw pass through
Remote to trunk g729 pass through (addressed by the
Trunk to local ulaw pass through
Trunk to remote g729 transcoding

Alternatively I could set trunk allow=g729,ulaw, which would prevent
transcoding for all inbound calls. Outbound from the local phone would use
the hook to change to ulaw.

I still don't have a way to enable the higher quality g722 codec for
internal use without making a transcoding mess. Maybe Asterisk 12 with
pjsip will have a better solution.

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