Bug 254198 – [MSE] readyState should change back to HAVE_METADATA when removing sample at current playtime

• Component: Media
• Status: RESOLVED FIXED

[Jean-Yves Avenard [:jya]]

This is similar to the side fix made in https://bugs.webkit.org/show_bug.cgi?id=254136
where we ensured that the readyState was updated before we fired `updateend`.

Per spec in the coded frame removal [1]
step5:
```
If this object is in activeSourceBuffers, the current playback position is greater than or equal to start and less than the remove end timestamp, and HTMLMediaElement.readyState is greater than HAVE_METADATA, then set the HTMLMediaElement.readyState attribute to HAVE_METADATA and stall playback.
```

This occurs before we return from the coded frame remove algorithm, so readyState should change before we fire the `updateend` event.

Note that there's a similar code flow for when evicting data. However due to how the MediaPlayer works in the GPU process this isn't currently achievable as the readyState change require a back and forth from CP to GPU Process, incompatible with the synchronous nature of the prepare append algorithm [2].

However, in practice it doesn't matter, as the eviction algorithm is designed in such a way that it will never evict data at the current time, and as such, the readyState can never move back to HAVE_METADATA

[1] https://w3c.github.io/media-source/#sourcebuffer-coded-frame-removal
[2] https://w3c.github.io/media-source/#sourcebuffer-prepare-append

[Radar WebKit Bug Importer]

<rdar://problem/106979551>

[Jean-Yves Avenard [:jya]]

Pull request: https://github.com/WebKit/WebKit/pull/11751

[EWS]

Committed 261955@main (20053bdeedfd): <https://commits.webkit.org/261955@main>

Reviewed commits have been landed. Closing PR #11751 and removing active labels.