Improve <video> and <audio> elements

From what I saw, most developers prefer third-party players (video.js, Plyr, etc.) over native <video> and <audio> elements for two reasons:

• style player
• add controls

Off the top of my head:

1. The speed of the audio/video playback can be set only via playbackRate property: document.getElementById('player').playbackRate = 0.5. Why not to expose it as UI control?

2. Whether the audio/video should start playing over again when it's finished can be set only via loop property: document.getElementById('player').loop = true or via loop attribute: <video src="test.webm" loop>. Why not to expose it as UI control?

3. There's no UI for switching sources (e.g. audio sources in different languages, video sources in different resolutions).

4. The <source> element has no srclang and label attrubutes unlike <track> element. You can't do something like:

<video width="320" height="240" controls>
  <source src="forrest_gump_480.mp4" type="video/mp4" label="480p">
  <source src="forrest_gump_1080.mp4" type="video/mp4" label="1080p" default>
  <source src="forrest_gump_en.ogg" type="audio/ogg" srclang="en" label="English" default>
  <source src="forrest_gump_no.ogg" type="audio/ogg" srclang="no" label="Norwegian">
  <track src="fgsubtitles_en.vtt" kind="subtitles" srclang="en" label="English" default>
  <track src="fgsubtitles_no.vtt" kind="subtitles" srclang="no" label="Norwegian">
</video>

Start by reviewing the native and elements and their existing controls, especially the playbackRate and loop properties and the entries shown in the issue. The proposal spans playback controls, source selection, and new source metadata, so the relevant specification entry points and a concrete scope must be established before implementation; done criteria are not defined.