So when I'm using MPV directly it works. So to be sure which file it doesn't find, I removed /usr/lib/python3.8/site-packages/vapoursynth.so and rerun MPV. And by doing so, I get the exact same issue as with emby theater. It can't initialize vapoursynth scripting.
That means while I'm using emby theater, Python doesn't find /usr/lib/python3.8/site-packages/vapoursynth.so
That's strange because /usr/lib/python3.8/site-packages is in my sys.path
I'm thinking, maybe while using mpv via emby theater it does run another python version (I also have python 2.7 installed)
Do you know if there is something I can do to make the mpv logs more verbose ?
And by the way, thanks for your help