1517030 - Screen sharing preview flickers whenever a selection is made

Status: NEW

(Firefox :: Site Permissions, defect, P3)

Description

[Jan-Ivar Bruaroey [:jib] (needinfo? me)]

Attachment: PreviewFlickering3.mov

(Probably the same cause as bug 1511416, but the symptoms are different and persistent)

Steps to reproduce (prep):
 1. Open https://jsfiddle.net/jib1/q75yb8pf/ in 10 tabs.
 2. In one of them, select "Entire Screen" to see preview, but leave the permission prompt open.
 3. Verify that a prompt is open in all 10 tabs (ignore bug 1511416)
 4. Open a new 11th tab but leave it blank (to prevent last content process from closing).
 5. Close the first 10 tabs.

 6. In the new tab, open https://jsfiddle.net/jib1/q75yb8pf/ and make some selections.

Expected result:
  The permission prompt preview updates to show each selection chosen.

Actual result:
  The permission prompt preview updates to show each selection chosen, but flickers a second or two.

  When it flickers, I see one or several of this error in stderr:

    JavaScript error: resource:///modules/webrtcUI.jsm, line 749: AbortError: The fetching process
    for the media resource was aborted by the user agent at the user's request.

  Sorta feels like there may be multiple active preview panels on top of each other?

  The symptom appears to grow worse each time a prompt is open in two tabs simultaneously. See attached video.

Workaround:
  The problem appears to persist until the last content process is closed.

Comment 1

[Johann Hofmann [:johannh]]

I have troubles running the fiddle, maybe because we're disallowing gUM to run in the null principal frame? Anyway, would you mind checking if this is still happening after bug 1511416? Thank you!

Comment 2

[Jan-Ivar Bruaroey [:jib] (needinfo? me)]

(In reply to Johann Hofmann [:johannh] from comment #1)

I have troubles running the fiddle, maybe because we're disallowing gUM to run in the null principal frame?

JSfiddle.net does not specify allow="display-capture" yet in its iframe, is the problem.

To work around it, in iframe area: right-click -> This Frame -> Show Only This Frame

to get to the following (or use this link directly):

https://fiddle.jshell.net/jib1/q75yb8pf/show/

When I try the steps in comment 0 with that url, then the problem is definitely still there.

Note that this opens the same screen-sharing prompt in multiple tabs, which does not seem affected by bug 1511416.