未捕获TypeError:无法读取null的属性“”getTracks“”

Question

我一直在尝试将webRTC广播源改为多对一

我认为一对多(广播)和多对一在这里有一点不同图像描述1：https://i.stack.imgur.com/zAzbt.png

他们有peerConnections，一切都很好。

呼叫者将MediaStream发送给所有被呼叫者。

所以我想

让我们从呼叫者到被呼叫者获取信令，并将MediaStream从被呼叫者传递到呼叫者。

所以我把这段代码放到被调用方

callee.js

socket.on('offer', (id, description) => {
  peerConnection = new RTCPeerConnection(config);
  navigator.mediaDevices
    .getUserMedia(constraints)
    .then((stream) => {
      video.srcObject = stream;
    })
    .catch((error) => console.error(error));

  let stream = video.srcObject;
  stream
    .getTracks()
    .forEach((track) => peerConnection.addTrack(track, stream));

  peerConnection
    .setRemoteDescription(description)
    .then(() => peerConnection.createAnswer())
    .then((sdp) => peerConnection.setLocalDescription(sdp))
    .then(() => {
      socket.emit('answer', id, peerConnection.localDescription);
    });

  peerConnection.onicecandidate = (event) => {
    if (event.candidate) {
      socket.emit('candidate', id, event.candidate);
    }
  };
});

caller.js

socket.on('answer', (id, description) => {
  peerConnections[id].setRemoteDescription(description);
  peerConnections.ontrack = (event) => {
    video.srcObject = event.streams[0];
  };
});

我从callee.js中得到了“未捕获TypeError:无法读取null的属性'getTracks‘”这个错误

你能给我一些建议吗？

谢谢

Answer 1

由于流是由Promise获取的，因此getTracks()将在getUserMedia()之前执行。因此，修改它，使其在promise之后执行。

exp:未测试

socket.on("offer", (id, description) => {
    peerConnection = new RTCPeerConnection(config);
    peerConnection.onicecandidate = event => {
        if (event.candidate) {
            socket.emit("candidate", id, event.candidate);
        }
    };
    navigator.mediaDevices
        .getUserMedia(constraints)
        .then(stream => {
            video.srcObject = stream;
            stream.getTracks().forEach(track => peerConnection.addTrack(track, stream));
        })
        .then(peerConnection.setRemoteDescription(description))
        .then(() => peerConnection.createAnswer())
        .then(sdp => peerConnection.setLocalDescription(sdp))
        .then(() => {
            socket.emit("answer", id, peerConnection.localDescription);
        })
        .catch(error => console.error(error));
});