What does browserSupportedMimes mean?

[skjnldsv]

browserSupportedMimes in lib/models/audios.ts and lib/models/videos.ts reads as a claim about what a browser can decode. It is not one, and some of what it lists no engine claims:

mime	canPlayType Chromium	Firefox	listed in
audio/vorbis	no	no	audios
audio/aacp	no	maybe	audios
video/mpeg	no	no	videos
video/x-flv	no	no	videos
video/quicktime	no	maybe	videos

Nothing is broken by that. The list decides which files the viewer offers to open; the handler then either plays the bytes or reports an error, and a media element reads the bytes rather than the declared type. #45 measured that end of it: one WAV served as audio/wav, audio/vnd.wave, audio/x-wav and application/octet-stream played in both engines, though canPlayType answers "no" for audio/vnd.wave.

So the question is what the list is meant to be, and the name should then say it:

• If it is what we route to the handler, then handledMimes or similar is the honest name, and entries like audio/vorbis are harmless but pointless: vorbis is a codec inside audio/ogg, not a container type a file carries.
• If it is what we expect to play, then it needs trimming, and that is a behaviour change for anyone whose files carry those types today.

Worth deciding once for both handlers rather than per pull request.