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?
In 2022 Mozilla seems to have the answer:
The Free Lossless Audio Codec (FLAC) is a lossless audio codec; there is also an associated simple container format, also called FLAC, that can contain this audio. The format is not encumbered by any patents, so its use is safe from interference. FLAC files can only contain FLAC audio data.
audio/flac audio/x-flac (non-standard)
So, depending on that I go with audio/flac. It seems to work for me on a Grav website.
