I have hundreds of playlists, some days-long, that run on my media machine. But if there are MKV files with subtitles VLC is displaying the subtitles all the time. It is distracting and I have to switch machines every time to turn the subtitles off. I don't want to disable subtitles at an app level, but within the playlists.

Logically the command line should be EXTVLCOPT sub-track=0 (none) or sub-track=none, but there is a pedantic 0 offset and -1 resets the list to system default.

I want English subtitles for foreign languages that I don't know, but not for those languages that I do.

I cannot find anywhere a comprehensive specification for M3U, or even a declared group responsible for the specifications.