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Supported codecs

WebRTC video:

• H264
• VP8
• VP9 (since WCS build 5.2.1908 and SFU SDK build 2.0.268)

WebRTC audio:

• Opus

Implementation basics

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In this case all the media traffic will pass through the WCS internal TURN server. This feature may be also used to wrap WebRTC traffic to TCP if the client has a bad channel, because WCS does not support TCP transport for SFU streams.

VP9 support

Since WCS build 5.2.1908 and SFU SDK build 2.0.

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268, VP9 codec is supported for SFU mediatraffic publishing and playback

codecs=opus,alaw,ulaw,g729,speex16,g722,mpeg4-generic,telephone-event,h264,vp8,vp9,flv,mpv

VP9 must be excluded for the cases when it is not supported by other party (SIP calls for instance)

codecs_exclude_sip=mpeg4-generic,flv,mpv,h265,vp9
codecs_exclude_sip_rtmp=opus,g729,g722,mpeg4-generic,vp8,vp9,mpv,h265

It is necessary to exclude H264 and VP8 codecs for SFU to enable VP9

codecs_exclude_sfu=alaw,ulaw,g729,speex16,g722,mpeg4-generic,telephone-event,h265,flv,mpv,vp8,h264,h265

VP9 codec allows to use SVC (Scalable Video Coding) at browser side by setting scalabilityMode in encoding profile

{
  "room": {
    ...
  },
  "media": {
    "audio": {
      "tracks": [
      ]
    },
    "video": {
      "tracks": [{
        "source": "camera",
        "width": 1280,
        "height": 720,
        "codec": "vp9",
        "encodings": [
          {
            "rid": "nonsense",
            "active": true,
            "scalabilityMode": "L1T3"
          }
        ]
      }]
    }
  }
}

In this example, a video track will be published in one resolution (L1) with 3 FPS layers (T3). A full scalability modes list is available here.

Known limits

1. It is not recommended to use Simulcast (using a number of encoding profiles) and SVC simultaneously because this may not be properly supported in a browser.

2. Only one spatial layer (L1) is available for screen sharing, other settings are ignored. The limit is hardcoded at WebRTC library level and applied in any browser.

Known issues

1. A stream captured from a screen window simulcast publishing will crash Chrome browser tab on minimizing this window

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