Andrea, you are Arch user, if you registered at their bug tracing system related to AUR can you look into this entry?
see discussion, it also must be noted this July Debian maintainer posted untested ffmpeg5 patch to Debian BTS but it was decided to disable ffmpeg support altogether ...
because I used lqtplay literally today while working on some cin-cv code ... I do not want this codebase die .....
can you post link to debian patch there?
and if possible test it? (my main system have ffmpeg 4.4.3 and termux might have some additional weirdness not accounted for)