No way to know if MediaStream/MediaStreamTrack ended after media device was disconnected

37 views

Skip to first unread message

Kostiantyn Tsaregradskyi

unread,

May 18, 2016, 5:16:51 AM5/18/16

to Temasys WebRTC Plugin

Hi,

while trying Temasys WebRTC plugin in Safari I've encountered situation when there is way to know if MediaStream/MediaStreamTrack ended after media device was disconnected.

Steps to reproduce

Open a webpage in Safari that requires Temasys WebRTC plugin to be installed, e.g.https://getaroom.io
Execute following code in console:

navigator.mediaDevices.enumerateDevices()
    .then(function(devices) {
        // maybe add some additional condition here that you select a webcam that you can unplug
        var device = devices.find(function(d) { return d.kind === 'videoinput' });

        navigator.mediaDevices.getUserMedia({ 
                video: { 
                    deviceId: device.deviceId, 
                    optional: [
                        { sourceId: device.deviceId }
                    ] 
                }
            })
            .then(function(stream) { 
                var video = document.createElement('video'); 
                document.body.appendChild(video); 
                attachMediaStream(video, stream);

                window.track = stream.getTracks()[0];
                window.stream = stream;

                console.log(window.stream.ended); // false
                console.log(window.track.enabled); // true
                console.log(window.track.readyState); // "live"

                window.stream.onended = function() {
                    console.log('stream ended');
                };

                window.stream.addEventListener('ended', function() {
                    console.log('stream ended');
                });

                window.track.onended = function() {
                    console.log('track ended');
                };

                window.track.addEventListener('ended', function() {
                    console.log('track ended');
                });
            });
    });

Just physically unplug your selected webcam.
Execute following code from console:

console.log(window.stream.ended); // false
console.log(window.track.enabled); // true
console.log(window.track.readyState); // "live"

Actual behavior:
There is no signs that stream or track is in ended state. track.readyState still says "live". No "ended" event handlers were fired.

Expected behavior:
At least some way to discover that track/stream was ended is required. E.g. similar code in Chrome will state that track.readyState equals to "ended" in this case. The life-cycle and "ended" state is described in the spec: https://www.w3.org/TR/mediacapture-streams/#track-ended

Other notes:
Firefox has no readyState property and "ended" events are not fired also, however there is a tricky way to determine that our track's device has ended or not by polling periodically for enumerateDevices() and comparing list of current devices with device used for track by comparing "label" + "kind" properties:

navigator.mediaDevices.enumerateDevices()
    .then(function(devices) {
        var deviceIsPresent = !!devices.find(function (d) {
                    return d.kind === window.track.kind + 'input' 
                    && d.label === window.track.label;
        });
    });

In Firefox and Chrome MediaStreamTrack's label property is the same as label property of device used for it (and it's according to spec - https://www.w3.org/TR/mediacapture-streams/#dom-mediastreamtrack-label). However this approach does not also work for Temasys, because for MediaStreamTrack label property it gives some encoded strings like "jxdbKnDYyl" or "nYGJNn7So0", while for devices from enumerateDevices() call it gives normal labels like "FaceTime HD-camera" or "Logitech C170" etc.

So it would be great if both situations are fixed:

- MediaStreamTrack should have correct readyState when associated media device is disconnected