[Webkit-unassigned] [Bug 225136] New: Short HLS video with 'loop' attribute stutters at the beginning of 3rd loop

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=225136

            Bug ID: 225136
           Summary: Short HLS video with 'loop' attribute stutters at the
                    beginning of 3rd loop
           Product: WebKit
           Version: Safari 14
          Hardware: iPhone / iPad
                OS: iOS 14
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Compositing
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: dylanjhaveri at gmail.com
                CC: simon.fraser at apple.com

Under the following conditions, the video stutters:

  - Using <video> element with a src that links to an HLS manifest that has multiple renditions
  - Using the `loop` attribute
  - Short video (~30 seconds-ish)

I tested this with multiple different sources. It doesn't appear to be an issue specific to one kind of video encoding or container format.

This is a demonstration with 4 different video sources:

Link: https://66vmt.csb.app/
Code: https://codesandbox.io/s/66vmt

Debugging:

  - I tried "manually" looping the video by avoiding the `loop` attribute and instead running javascript that listens for the player 'ended' event and calls play(). This did not help
  - The bug doesn't seem to happen on older iPhone (couldn't get it to happen with iPhone 8)
  - I tried with a single-rendition HLS manifest, same bug

This is my first time filing a Safari bug, is this the right place and is "Compositing" the correct component? It was the only component I found that mentioned video.

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