I have also problem that some movies doesn’t play smoothly on pi 4b. But for now its only on 1080p files with VC-1 Format, 4K works fine. The sources are untouched, video as audio also.
I could see, that in this moment the CPU usage was at the level 100-115%. So far its smaller then ~94% movie plays really smoothly.
I’ve tried already with and without mmal- HW decoding. Also options with sync video to display.
My audio is as pass-through but I also tried without it. It also doesn’t matter if audio is AC-3, DTS, DTS-HD etc.
With license for hardware decode on my “old” pi 3b+ it works best.
Version I’m using: LibreELEC-RPi4.arm-9.1.501
have you some suggestions?