James Cloos writes:

> >> baresip and webrtc sip clients specify opus codec like this:
> 
> >> a=rtpmap:96 opus/48000/2.
> >> a=fmtp:96 stereo=1;sprop-stereo=1.
> 
> >> whereas sems does it like this:
> 
> >> a=rtpmap:105 opus/48000.
> 
> SS> I noticed that, too, but I've had audio issues with e.g. using sems
> SS> echo or conference with stereo clients in master.
> 
> To be consistant with draft-ietf-payload-rtp-opus-03.txt, sems ought to
> use:
> 
>     a=rtpmap:105 opus/48000/2
> 
> The two sides should be able to negotiate stereo=0 provided that the
> rtpmap is opus/48000/2.  (Note that on its own opus/48000/2 is mono,
> even though it looks like stereo.)

so when sems receives

  a=rtpmap:96 opus/48000/2
  a=fmtp:96 stereo=1;sprop-stereo=1

it should accept it and reply with

  a=rtpmap:96 opus/48000/2

stereo and sprop-stereo params are not needed in reply because they
both default to 0.

still, this reply does not guarantee that caller will actually sends
mono signals.

-- juha
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