equivocal

The issue is that the docker service runs as root and their defaults added the user to a group that allows them to control that service without sudo

So, the root filesystem can just be passed as a volume to a container and then do whatever you want from there.

So, quick testing is that mpv will pull subtitles by default but not display them without cycling the track (with J) or setting slang with an available language code[s]. (with slang=en,en-US for English.) Although, it will completely ignore auto-generated subtitles.

I did find that ytdl-raw-options='sub-langs="en,en-US",write-sub=,write-auto-sub=' will also give the option to use auto-generated subs.

I’m not too familiar with SMPlayer but I was seeing that you can use an mpv.conf with it.