Some software uses audio/flac. Some uses audio/x-flac.
MDN suggests that x-flac is "non-standard". But based on what?
But this appears to be the official registry for audio/ types... and audio/flac doesn't appear on it. Has nobody ever registered flac there? Whyever not?
In 2021, what is the correct place to determine the list of "standard" content-types, and what is it for FLAC?
But this appears to be the official registry for audio/ types... and audio/flac doesn't appear on it. Has nobody ever registered flac there? Whyever not?
One cannot just register a media type. It can only be registered when an IETF document has need of it. A document describing the FLAC format has just been approved, so today, the audio/flac media type has been added to the registry.
So, from today, "audio/flac" is official, though many applications have been using it for years already.