[Freeswitch-users] Confused about codecs?

Mon Sep 27 07:58:51 UTC 2021

Hi Allan,

this is a very simple logical bug which exists in Asterisk (and 
apparently in FreeSwitch).
If you allow for multiple codecs, Asterisk will just start with one, but 
once it gets a frame from the other side with a different codec, it will 
switch to that codec. If both sides do that, they start with different 
codecs and the latency is high enough, they'll get semi-stuck in a codec 
switching loop until one frame gets lost.

The proper bugfix would be to keep the codec choice "sticky" and not to 
change the codec on every packet. (e.g. wait for n packets with a new 
codec before you change to that codec) One side doing that should solve 
the problem.

The workaround, as mentioned before, is to limit the codecs you speak, 
but that will likely give you other slight problems regarding voice quality.

Bye
   Christian Berger

Am 26.09.21 um 22:23 schrieb Allan Kristensen:
> Hello,
> 
> We are getting these weird log messages from FS and I'm a little 
> uncertain what they are (there are thousands being logged), can someone 
> clarify?
> 
> September 23rd 2021, 10:35:40.849 ms-euc1-1a 
> 28423364-1c49-11ec-b0ec-e3438dde9495 2021-09-23 08:35:40.844181 
> [WARNING] switch_core_media.c:3305 Changing current codec to PCMU 
> (payload type 0).
> September 23rd 2021, 10:35:40.749 ms-euc1-1a 
> 28423364-1c49-11ec-b0ec-e3438dde9495 2021-09-23 08:35:40.744202 
> [WARNING] switch_core_media.c:3305 Changing current codec to PCMA 
> (payload type 8).
> September 23rd 2021, 10:35:40.669 ms-euc1-1a 
> 28423364-1c49-11ec-b0ec-e3438dde9495 2021-09-23 08:35:40.664168 
> [WARNING] switch_core_media.c:3305 Changing current codec to PCMU 
> (payload type 0).
> September 23rd 2021, 10:35:40.569 ms-euc1-1a 
> 28423364-1c49-11ec-b0ec-e3438dde9495 2021-09-23 08:35:40.564190 
> [WARNING] switch_core_media.c:3305 Changing current codec to PCMA 
> (payload type 8).
> September 23rd 2021, 10:35:40.489 ms-euc1-1a 
> 28423364-1c49-11ec-b0ec-e3438dde9495 2021-09-23 08:35:40.484194 
> [WARNING] switch_core_media.c:3305 Changing current codec to PCMU 
> (payload type 0).
> September 23rd 2021, 10:35:40.389 ms-euc1-1a 
> 28423364-1c49-11ec-b0ec-e3438dde9495 2021-09-23 08:35:40.384180 
> [WARNING] switch_core_media.c:3305 Changing current codec to PCMA 
> (payload type 8).
> September 23rd 2021, 10:35:40.309 ms-euc1-1a 
> 28423364-1c49-11ec-b0ec-e3438dde9495 2021-09-23 08:35:40.304190 
> [WARNING] switch_core_media.c:3305 Changing current codec to PCMU 
> (payload type 0).
> 
> I'm thinking it's because we are receiving RTP packets with both types 
> from remote?
> 
> It only happens for a specific provider, so I'm thinking it's them, I 
> just need to tell them the problem is.
> During codec negotiations we offered PCMA + PCMU and the SDP response 
> from them also had PCMA + PCMU, that means we can choose what we want 
> right? not that they should send us both? ;-)
> 
> Thank you...
>     Allan
> 
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Christian Berger

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