Bug 274195 – [MSE] If src attribute is defined, ignore source alternative

• Component: Media
• Status: RESOLVED FIXED

[Jean-Yves Avenard [:jya]]

Per spec, if a media element has a src attribute defined, `<source>` are ignored [1] as a consequence of the media source selection algorithm [2]

step 6:
```
⌛ If the media element has an assigned media provider object, then let mode be object.

⌛ Otherwise, if the media element has no assigned media provider object but has a src attribute, then let mode be attribute.

⌛ Otherwise, if the media element does not have an assigned media provider object and does not have a src attribute, but does have a source element child, then let mode be children and let candidate be the first such source element child in tree order.
```

Currently, to check if we have a remote playback alternative, we only check if a playable alternative source is defined, and if so allow playback. But if a src (or srcObject) is defined, when selecting an AirPlay target those sources will be ignored.

So we need HTMLMediaElement::hasWirelessPlaybackTargetAlternative() to return false unless `m_loadState != LoadingFromSourceElement`

[1] https://html.spec.whatwg.org/multipage/media.html#attr-media-src
[2] https://html.spec.whatwg.org/multipage/media.html#concept-media-load-algorithm

[Jean-Yves Avenard [:jya]]

rdar://128098363

[Jean-Yves Avenard [:jya]]

Pull request: https://github.com/WebKit/WebKit/pull/28584

[EWS]

Committed 278834@main (fb01f8840fd2): <https://commits.webkit.org/278834@main>

Reviewed commits have been landed. Closing PR #28584 and removing active labels.