[SIP Beyond VoIP] Stereo with sylk-webrtc

Tijmen de Mes tijmen at ag-projects.com
Fri Mar 9 17:06:28 CET 2018


I think it all depends on who/what you are calling. Does the stereo not work when having an audio between Party A and Party B both on WebRTC, or does it not work when having a Video conference?

Without modifying anything, I see Firefox already sending stereo=1 when making a call (local SDP), for chrome I don’t see it right now.

Best regards,

Tijmen de Mes
AG Projects

> On 9 mrt. 2018, at 14:15, Penelope Vennisse <studio.pqv9 at gmail.com> wrote:
> Hi, we've been trying for a couple of days to get stereo working in Chrome with the sylk-webrtc browser project. Modifying the SDP and setting echoCancellation to false have not had any effect. Is there a known issue with sylk-webrtc and sylkserver, for stereo with OPUS? Appreciate any feedback.
> We've tried what works for other webrtc apps:
> 1. Force Chrome to disable audio processing:
> constraints.audio = {
>             mandatory: {
>                 echoCancellation: false
>             }
>         };
> 2. Set the SDP to prefer OPUS, add stereo and high-bitrate. We also tried removing all other codecs to see if that helped.
> v=0
> o=- 2951467701722993374 2 IN IP4
> s=-
> t=0 0
> a=msid-semantic:  WMS
> a=group:BUNDLE audio
> m=audio 9 RTP/SAVPF 111
> c=IN IP4
> a=rtpmap:111 opus/48000/2
> a=fmtp:111 minptime=10;useinbandfec=1; stereo=1; sprop-stereo=1; maxplaybackrate=524288; sprop-maxcapturerate=524288; maxaveragebitrate=524288
> a=rtcp:9 IN IP4
> a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
> a=setup:active
> a=mid:audio
> a=recvonly
> a=ice-ufrag:Q2dY
> a=ice-pwd:ixK6U9znPvXZeQCOzUZSJgJ/
> a=fingerprint:sha-256 9D:32:5E:A5:06:6C:01:53:C4:BE:08:F9:6B:F2:3D:83:CD:F6:51:B9:A4:5B:F1:34:F9:13:B4:C3:60:9F:2C:F6
> a=rtcp-mux
> The connection works fine and the audio is using the bitrate directive, but it's always mono. Advice is welcome! We've verified that stereo works in the browser with other apps, for example the appr.tc <http://appr.tc/> reference app using https://appr.tc/r/955394799?stereo=true&audio=echoCancellation=false <https://appr.tc/r/955394799?stereo=true&audio=echoCancellation=false>
> (Note that Chrome 65 and up currently has a stereo regression bug so we're testing in Chrome 59 using Electron until that's resolved)
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