[Freeswitch-dev] Codec change from PCMA to PCMU within a running freeswitch session

Brian West brian at freeswitch.org
Fri Mar 7 16:51:49 MSK 2014

Sounds like you need to test against master, if the problem is still there then you’ll need to report a bug on jira.freeswitch.org.

Brian West
brian at freeswitch.org
FreeSWITCH Solutions, LLC
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On Mar 7, 2014, at 5:41 AM, Achim Stamm <stamm at lyth.de> wrote:

> Hello!
> I have following problem:
> My current session is connected to a third-party Application by using an own Freeswitch application "DoingReadAndWriteFrames". The communication between Freeswitch Session and third-party application is done by reading and writing frames in a while loop.
> At start of Freeswitch session the codec is PCMA, which I need for voice recognition.
> Customer reports, that the codec of the Freeswitch session changes from PCMA to PCMU.
> If an external call comes in, I’m playing an audio ringing tone into the Freeswitch session.
> I have realize, that the codec is changed back from u-law to a-law.
> I have recorded the voice stream and I have heard the codec change.
> I have never reproduced the codec change of an active Freeswitch session on my test system.
> Some customer reports, that the system is running fine (no codec change) for half a year.
> My own bug fix is to manually translate PCMU data to PCMA, if session codec is switched to PCMU.
> But I cannot test my bug fix, because I can't force the changing of codec within a running session.
> Maybe the "codec change" was a bug from Freeswitch version at October 2010.
> Maybe the hardware SPA3102 sends a sip re-invite message on special cases.
> I have no idea.
> I have some questions about codec negotiation and sip re-invite:
> A) On what reasons can a re-invite message triggered and why is the session codec changed?
> B) What must be happen, that a codec is changing, after a codec negotiation was done, on a running Freeswitch session?
> C) Why is there a codec change back to a-law, when I’m playing an own ringing tone?
> D) Is there a solution for forcing Freeswitch always use PCMA?
> My configuration of Freeswitch in “vars.xml” to force codec PCMA:
> <X-PRE-PROCESS cmd="set" data="global_codec_prefs=PCMA"/>
> <X-PRE-PROCESS cmd="set" data="outbound_codec_prefs=PCMA"/>
> Greetings
> Achim Stamm
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