ffmpeg, nonfree + other goodness.

[eladkarako]

didn't find many guides for nonfree,
some targeting raspberry-pi might be helpful,
and there might be docker with patches such as https://github.com/nanake/ffmpeg-tinderbox/releases (but, for arm/arm64).
eventually I've just used some assets from an apk..
(see https://github.com/Magisk-Modules-Repo/ccbins/issues/7 )

feel free to update here, if you've got nice guides with as much as non-free libs as possible :]