[Webkit-unassigned] [Bug 229611] New: MediaRecorder with canvas captureStream() produces blank video

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=229611

            Bug ID: 229611
           Summary: MediaRecorder with canvas captureStream() produces
                    blank video
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Media
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ashley at scirra.com

Using MediaRecorder to record a MediaStream from the canvas captureStream() method appears to only produce a blank video in Safari 15 / TP 130 on macOS 12 beta (21A5304g).

Demo URL: https://downloads.scirra.com/labs/screenrecording/

Steps to reproduce:

1. Click 'Record canvas'
2. Wait a few seconds
3. Click 'Stop recording'

A video file will then be downloaded.

Observed result:
The video has the expected duration, but just displays all black.

Expected result:
Video to show canvas content that was recorded.

Other notes:
This appears to work correctly on iOS 14, so may be unique to macOS. Also note we have reports that a flickery video is recorded on Safari 14 on macOS, but we can't easily test that right now. Finally the 'Record screen' option - using getDisplayMedia() - appears to work correctly, so this looks like an issue specific to using MediaRecorder with canvas captureStream().

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