[SR-Users] RTPEngine / Transcoding question

Carsten Bock carsten at ng-voice.com
Tue May 21 17:48:15 CEST 2019


Hi,

I want to implement selective transcoding, e.g. avoiding Transcoding
between a HD codec (G722) and a non HD Codec (G711).

In case the caller does offer HD codecs, this is fine, e.g.

if(sdp_with_codecs_by_name("G722,OPUS")) {
  rtpengine_offer("codec-transcode=OPUS codec-transcode=G722
codec-transcode=PCMA");
} else {
  rtpengine_manage("codec-transcode=PCMA");
}

Now I have the issue, if the callee only sends me G711, I don't want to
offer G722 or Opus to the caller. However, rtpengine_answer() does not seem
to accept "codec-strip=G722 codec-strip=OPUS", e.g.:

onreply_route() {
  if(!sdp_with_codecs_by_name("G722,OPUS")) {
    rtpengine_ manage("codec-strip=OPUS codec-strip=G722");
  }
}

As a result, the SDP always contains the transcoding options, e.g. G722 and
OPUS. I always end up in transcoding G722 to G711, which is meaningless in
that case.

Any ideas on how to solve that?
(above examples very simplified)

Thanks,
Carsten
--
Carsten Bock I Managing Director
ng-voice GmbH

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