在 WebRTC 连接中检测离线对等点

Question

We are developing a video stream from a mobile device to a computer using WebRTC. The mobile device might lose its connection completely and the computer should be able to detect that. Right now, the video just freezes. But neither of the EventHandler s of RTCPeerConnection are called in such a situation.

• So how can such a connection failure be detected on the other peer?
• How can a peer detect connection problems on connection establishment in the first place?

Answer 1

As a workaround in Firefox, you could use getStats to detect if packets stop coming in:

var findStat = (m, type) => [...m.values()].find(s => s.type == type && !s.isRemote);

var hasConnected = new Promise(resolve => pc.oniceconnectionstatechange =
  e => pc.iceConnectionState == "connected" && resolve());

var hasDropped = hasConnected.then(() => new Promise(resolve => {
  var lastPackets = countdown = 0, timeout = 3; // seconds

  var iv = setInterval(() => pc.getStats().then(stats => {
    var packets = findStat(stats, "inbound-rtp").packetsReceived;
    countdown = (packets - lastPackets)? timeout : countdown - 1;
    if (!countdown) resolve(clearInterval(iv)); 
    lastPackets = packets;
  }), 1000);
}));

Here's a demo: https://jsfiddle.net/4rzhe7n8/

Answer 2

the iceconnectionstatechange handler should fire after ~5-10 seconds of not receiving data from the peer anymore (in Chrome; Firefox is working on that currently). See https://webrtc.github.io/samples/src/content/peerconnection/states/ for an example.