firefox specify current window to stream with getUserMedia

Question

In firefox, I'm able to request a video stream of a window with

navigator.mediaDevices.getUserMedia({
    video: {
      mediaSource: 'window',
    },
})

This produces a dialog like this:

I only care about the current window. Is there a way to specify in my call to getUserMedia that I would like the current tab (or window) only?

Answer 1

I don't think so no...

What FF implements here is not really specified yet, but w3c is working on a new API which will take care of Screen Capture: MediaDevices.getDisplayMedia.

While it's not what Firefox did implement, there is a clear paragraph in this paper about why deviceId can't and will not work on such requests:

Each potential source of capture is treated by this API as a discrete media source. However, display capture sources MUST NOT be enumerated by enumerateDevices, since this would reveal too much information about the host system.

Display capture sources therefore cannot be selected with the deviceId constraint, since this would allow applications to influence selection; setting deviceId constraint can only cause the resulting MediaStreamTrack to become overconstrained.

So, once again even if FF does not implement this API yet, we can assume they do follow this same rule for their current implementation, for the same reasons.

However, what will apparently be possible to do when this API will come to life, is to use the "browser" constraint, instead of "window". While the specs are not really clear as to what it is exactly ("a browser display surface, or single browser window"), I guess it will be closer to what you want than "window", and someone even asked 2 days ago for a "tab" constraint, could we even hope for a "current-tab" constraint? _{That might need someone to open an issue on w3c github's page.}