Maybe install 2.1.34-alternate for now as mplayer doesn’t seem to cause the freezing issue.
About media sync, I’d recommend to watch new intro videos about syncing.
And if I correctly understood the issue with the hotkeys, they only work in Anki, i.e. they should work just fine with the audio file, but with the video file the hotkeys will only work if Anki window is active, i.e. focused.
The freezing issue is yet to be investigated. I tried a different backend for mpv video player as a temporary workaround - https://ankiweb.net/shared/info/100620900 (Video Fix 2) - but it didn’t go well, Anki can only be closed from the task manager and I couldn’t quickly find where is the problem, but it looks like the freezing issue is still there.
The freezing issue seems to be possible to reproduce with a short video clip like this one - Gofile - Your all-in-one storage solution - it seems to be a bit random and might take some time to trigger it.
I’m not sure if I’ll be able to handle it, but I’ll try to find a way to fix it, or maybe a possible workaround, over the weekend.