I have a simple RTCPeerConnection between two peers, to stream video.

The connection works perfectly with MediaStream types. Video and camera streams are going through and received.

However, when I try to send a MediaStream that contains a CanvasCaptureMediaStreamTrack, nothing useful comes out of pc2, the receiving peer. A MediaStream arrives, but when I attach it to a <video> element, it shows nothing (not even a blank picture), and a MediaRecorder also records nothing (0 bytes). At the same time, there seems to be a video track in the stream.

The canvas isn't empty. It has a width of 320x200, and contains a filled rectangle, with a text on it. I can send the captured canvas stream directly to a <video> element, and it appears correctly.

It's apparently not impossible to send a CanvasCaptureMediaStreamTrack through an RTC connection, as it's demonstrated here: https://webrtc.github.io/samples/src/content/capture/canvas-pc/

When I looked into the source code, I saw nothing new. This is how the demo captures the canvas stream, and passes it to the RTCPeerConnection:

const pc1 = new RTCPeerConnection(null);
const stream = canvas.captureStream();

stream.getTracks().forEach(track => {
  pc1.addTrack(track, stream);
});

Is there something I'm missing? Why won't my canvas stream go through the connection, while the demo works?