webrtc/protocol/additional-codecs.html

<!doctype html>
<meta charset=utf-8>
<title>Send additional codec supported by the other side</title>
<meta name=timeout content=long>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="../RTCPeerConnection-helper.js"></script>
<script>
'use strict';
// Tests behaviour from
// https://www.rfc-editor.org/rfc/rfc8829.html#section-5.3.1
// in particular "but MAY include formats that are locally
// supported but not present in the offer"

promise_test(async t => {
  const pc1 = new RTCPeerConnection();
  t.add_cleanup(() => pc1.close());
  const pc2 = new RTCPeerConnection();
  t.add_cleanup(() => pc2.close());
  exchangeIceCandidates(pc1, pc2);

  const stream = await getNoiseStream({video: true});
  t.add_cleanup(() => stream.getTracks().forEach(t => t.stop()));
  pc1.addTrack(stream.getTracks()[0], stream);
  pc2.addTrack(stream.getTracks()[0], stream);
  // Only offer VP8.
  pc1.getTransceivers()[0].setCodecPreferences([{
    clockRate: 90000,
    mimeType: 'video/VP8'
  }]);
  await pc1.setLocalDescription();

  // Add H264 to the SDP.
  const sdp = pc1.localDescription.sdp.split('\n')
    .map(l => {
      if (l.startsWith('m=')) {
        return l.trim() + ' 63'; // 63 is the least-likely to be used PT.
      }
      return l.trim();
    }).join('\r\n') +
    'a=rtpmap:63 H264/90000\r\n' +
    'a=fmtp:63 level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=42e01f\r\n'
  await pc2.setRemoteDescription({
    type: 'offer',
    sdp: sdp.replaceAll('VP8', 'no-such-codec'), // Remove VP8
  });
  await pc2.setLocalDescription();
  await pc1.setRemoteDescription(pc2.localDescription);

  await listenToConnected(pc2);
  const stats = await pc1.getStats();
  const rtp = [...stats.values()].find(({type}) => type === 'outbound-rtp');
  assert_true(!!rtp);
  assert_equals(stats.get(rtp.codecId).mimeType, 'video/H264');
}, 'Listing an additional codec in the answer causes it to be sent.');
</script>