[Webkit-unassigned] [Bug 262617] New: Video frame shifts when played before buffer begins using HLS

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=262617

            Bug ID: 262617
           Summary: Video frame shifts when played before buffer begins
                    using HLS
           Product: WebKit
           Version: Safari 16
          Hardware: Mac (Apple Silicon)
                OS: macOS 13
            Status: NEW
          Severity: Blocker
          Priority: P2
         Component: Media
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: cglavin at adobe.com

Created attachment 468062

  --> https://bugs.webkit.org/attachment.cgi?id=468062&action=review

This is an example from a code sandbox where a portrait video frames should take up the width and height of the video element, but they are shifted up and sometimes squished in dimensions

Repro steps:
- hit the play button before buffer begins
- seek around to unbuffered zones
- try again and again

Expected:
- Video plays once buffered and takes up the full video element container

Actual:
- Video frame fluctuates in size, sometimes squishing the aspect ratio and then resizing up (or, sometimes we were noticing it shift to the left) 


Notes:
- from within our app, we were not able to reproduce this when we removed the poster attribute (but that is not desired)
- we haven't been able to reproduce in Safari 17



Example of the repro code:

<div className="App">
      <video
        controls={true}
        width="270px"
        height="480px"
        src="path/to/hls/manifest"
      />
</div>

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