Scalable Video Codec include an SVC support check

[opusonline]

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Browser affected

Browser name including version (e.g. Chrome 64.0.3282.119)
Google Chrome 110.0.5481.77

Description

Add a check if SVC is supported in the current browser to the SVC sample, since even Chrome >= 101 will report supported: true in MediaCapabilities.encodingInfo() with scalabilityMode. But SVC is only supported in Chrome >= 111 (see https://chromestatus.com/feature/5769626174619648).

The only way I could find to check this, is something like:

() => {
  let supported = false;
  try {
      const pc = new RTCPeerConnection();
      const scalabilityMode = 'L2T2';
      const transceiver = pc.addTransceiver('video', { sendEncodings: [{ scalabilityMode }] });
      const parameters = transceiver.sender.getParameters();
      const [encoding] = parameters.encodings || [];
      supported = Boolean(encoding && encoding.scalabilityMode === scalabilityMode);
  } catch (error) {
      console.error(error);
  }
  return supported;
};

Steps to reproduce

Open the SVC sample https://webrtc.github.io/samples/src/content/extensions/svc/ in a Chrome browser >=101 and < 111. Click the "Start button", allow camera access, select "video/VP8" as Codec preferences.

Expected results

Since SVC is not supported in Chrome < 111, the list of scalability modes should be empty.

Actual results

The list of scalability modes include L1T1, L1T2, and L1T3.

[Orphis]

This is a browser bug where the MediaCapabilities would report that the encoders are technically able to do SVC but the WebRTC encoders are not able to be configured for SVC.

It is also an issue for browsers implementing the Media Capabilities API partially and don't read the scalabilityMode query, but would still answer "supported: true", which could possibly be avoided by making sure the "question" could be integrated in the response.