Trascoding in 2 x 183 with different codecs scenario
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Stefan Mititelu
Apr 17, 2026, 5:05:45 AM (12 days ago) Apr 17
to Sipwise rtpengine
Hello!
We are in the process of upgrading rtpengine from 11.5 to 14.1
We've noticed a behavior change in transcoding for the below scenario:
1. INVITE (offer with multiple codecs e.g. G729, PCMA etc...)
2. 183 (answer with e.g. G729 codec)
3. 183 (answer with e.g. PCMA codec, same to-tag as previous one)
4. 200 (answer with e.g. PCMA codec, same to-tag as previous ones)
For same ng control channel options: we only use passthrough, so nothing explicitly set in ng control, related to transcoding:
- Version 11.5: transcoded PCMA to G729 automatically, without anything special set
- Version 14.1: does not automatically transcode PCMA to G729 for this scenario
Since main goal is only to upgrade rtpengine version, we'd like as much as possible to keep same behavior as previous version.
Do you got any tips for achieving this, either on ng control channel or on source code?
..so far been trying to:
1. add some ng transcoding flags at answer time, without any success
2. setting "codec-accept=all" at offer time, which worked for the above scenario and heard PCMA/G729 transcoded media, but definitely we'd like to keep passthrough as much as possible
Thank you,
Stefan Mititelu
We are in the process of upgrading rtpengine from 11.5 to 14.1
We've noticed a behavior change in transcoding for the below scenario:
1. INVITE (offer with multiple codecs e.g. G729, PCMA etc...)
2. 183 (answer with e.g. G729 codec)
3. 183 (answer with e.g. PCMA codec, same to-tag as previous one)
4. 200 (answer with e.g. PCMA codec, same to-tag as previous ones)
For same ng control channel options: we only use passthrough, so nothing explicitly set in ng control, related to transcoding:
- Version 11.5: transcoded PCMA to G729 automatically, without anything special set
- Version 14.1: does not automatically transcode PCMA to G729 for this scenario
Since main goal is only to upgrade rtpengine version, we'd like as much as possible to keep same behavior as previous version.
Do you got any tips for achieving this, either on ng control channel or on source code?
..so far been trying to:
1. add some ng transcoding flags at answer time, without any success
2. setting "codec-accept=all" at offer time, which worked for the above scenario and heard PCMA/G729 transcoded media, but definitely we'd like to keep passthrough as much as possible
Thank you,
Stefan Mititelu
Richard Fuchs
Apr 17, 2026, 8:10:00 AM (12 days ago) Apr 17
to rtpe...@googlegroups.com
On 17/04/2026 05.05, 'Stefan Mititelu' via Sipwise rtpengine wrote:
> Do you got any tips for achieving this, either on ng control channel
> or on source code?
IIRC either the `no codec renegotiation` flag or the `static codecs`
> Do you got any tips for achieving this, either on ng control channel
> or on source code?
flag exist for this purpose, possibly combined with `single codec`
and/or `allow transcoding`. Off the top of my head 😁
Cheers
Stefan Mititelu
Apr 20, 2026, 6:29:48 AM (9 days ago) Apr 20
to rtpe...@googlegroups.com
Thanks for the tips! So far I did not manage to make it work using the flags.
Issue is starting with this commit [1] (first commit after "Release 13.1.0.0", from 13.5.1 LTS branch), which looks like a big feature with quite a few follow-up commits.
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