Disabling DRMPRIME in the expert settings solved the problem for me.
I wasn't aware that the hardware decoders can have such an impact on system stability. If the decoder stops playing my (maybe broken/non-standard) ile -> ok. But, freezing the whole RPi4?
Can you be more specific. There are a few combinations of options here that will narrow it down. You have:
1) Allow using DRM PRIME decoder
2) Allow hardware acceleration with DRM PRIME
3) PRIME render method
The default is 1=enabled, 2=enabled and 3=direct which you've reported as hangs
Can you test:
1=enabled, 2=enabled, 3=EGL
1=enabled, 2=disabled, 3=direct
1=enabled, 2=disabled, 3=EGL
1=disabled, 2=N/A, 3=EGL
As chewitt says, provide us with an example file. Ideally cut one down to a couple of minutes, confirm issue still occurs and upload it somewhere (e.g. google drive).
If you believe it occurs with all files, then can you test a publicly available file (e.g. Big Buck Bunny and confirm you still see the issue?