Hi there,
sorry, my english is not very good and i don't know much about codecs and so on, but i think i have the same problem...
Just want to let you know this...
i have a Tictid K12 (S912) box and with Libreelec 11.0.1 i can't play 4k videos from my NAS drive.
Rebooting the Device and starting 4k Video the first time it runs.
Then Starting a 1080 Video and Stopping.
Starting the same 4k Video that runs - box is crashing - no ssh
Played with some Settings (Refresh rate) the box is not crashing but after a few seconds 4k Video plays with massive errors or stops or don't start the video. I just gave up with testing...
With Coreelec 9.2.8 Video playback 4k from my NAS drive works very well...