[Webkit-unassigned] [Bug 187677] New: Local MediaStream cloned video stops playing when original stream video is hidden/redisplayed

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=187677

            Bug ID: 187677
           Summary: Local MediaStream cloned video stops playing when
                    original stream video is hidden/redisplayed
           Product: WebKit
           Version: Safari 11
          Hardware: iPhone / iPad
                OS: iOS 11
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebRTC
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: webkit at xylil.com
                CC: youennf at gmail.com

Test case here:

https://staging-connect.circleanywhere.com/public/ios/local-video-copy-display-bug/

Steps to reproduce:

1. Load the page, notice that the local MediaStream-backed video properly autoplays.
2. Click the 'Toggle local' button to hide the video, click again to redisplay. Notice that the video continues to properly autoplay.
3. Click the 'Copy local' button. This uses the MediaStream.clone() method to copy the stream, remove the audio track, and display the cloned stream in another video element. Notice that both the original MediaStream-backed video and the cloned MediaStream-backed video properly autoplay.
4. Click the 'Toggle local' video button, notice that the cloned MediaStream-backed video continues to properly autoplay.
5. Click the 'Toggle local' video button, notice that the original MediaStream-backed video autoplays, but the cloned MediaStream-backed video does NOT.

According to https://webkit.org/blog/7763/a-closer-look-into-webrtc/, "MediaStream-backed media will autoplay if the web page is already capturing", so the fact that the cloned stream stops playing violates this policy.

This bug is troublesome in more complex video applications, where it's cleaner design to display different copies of the same MediaStream than to move video elements around in the DOM.

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