WebRTC: Detecting muted track faster post warm-up - webrtc

Question

I'm warming up my transceiver like so:
pc.addTranceiver('video')
This creates a dummy track in the transceiver's receiver. Soon after, the unmute event fires on that track.
Then, ~3 seconds later, the mute event fires.
My goal is to detect that a track is a dummy track as fast as possible.
ideas
send a message via the data channel telling the peer that the track is void. this is a pain since i'll have to send another message when I later call replaceTrack
write a frame of the track to canvas & see if it's an image. This seems really barbaric, but it's faster than 3 seconds.
anything better? it feels like this should be pretty simple.

Answer 1

This is a bug in Chrome (please ★ it so they'll fix it).
The spec says receiver tracks must start out muted and should stay that way until packets arrive. But Chrome fires the unmute event immediately, followed a few seconds later by a mute event due to inactivity (another bug):
const config = {sdpSemantics: "unified-plan"};
const pc1 = new RTCPeerConnection(), pc2 = new RTCPeerConnection();
pc1.addTransceiver("video");
pc2.ontrack = ({track}) => {
console.log(`track starts out ${track.muted? "muted":"unmuted"}`);
track.onmute = () => console.log("muted");
track.onunmute = () => console.log("unmuted");
};
pc1.onicecandidate = e => pc2.addIceCandidate(e.candidate);
pc2.onicecandidate = e => pc1.addIceCandidate(e.candidate);
pc1.onnegotiationneeded = async e => {
await pc1.setLocalDescription(await pc1.createOffer());
await pc2.setRemoteDescription(pc1.localDescription);
await pc2.setLocalDescription(await pc2.createAnswer());
await pc1.setRemoteDescription(pc2.localDescription);
}
In Chrome you'll see incorrect behavior:
track starts out muted
unmuted
muted
In Firefox you'll see correct behavior:
track starts out muted
Chrome workaround:
Until Chrome fixes this, I'd use this workaround:
const video = document.createElement("video");
video.srcObject = new MediaStream([track]);
video.onloadedmetadata = () => log("unmuted workaround!");
Until this fires, assume the track to be muted.