[Webkit-unassigned] [Bug 240549] New: Duplicated cues of in-manifest captions, if cue properties modified

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=240549

            Bug ID: 240549
           Summary: Duplicated cues of in-manifest captions, if cue
                    properties modified
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Media
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: webkit at gkatsev.com

If, when, playing back an HLS stream with in-manifest captions, a cue's properties are modified, when seeking back and replaying the video so that the cue becomes active again, the cue becomes duplicated.
Modifying any property of the cue will cause a new cue to be re-added with the original values and both of them to be displayed.

I have a live example here https://simple-video.netlify.app/double-cues.html
It waits for some cues to be available, modifies their `line` properties to be `0` and then seeks back. On the second play, there are now cues at the top and the bottom of the display area.

To me, this seems a bit unexpected that a new cue is created even though the original reference still exists, even if it was modified.
I'd expect no new cues to be created.

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