Ok, after like 15hours of playing with it, I got out of ideas, so I'm gonna ask here.
I've installed the latest ubuntu mate 20.10 64bit (+ did all app upgrades), fixed audio problem with pulseaudio, set 4kp60, set gpu_mem 256, followed this https://www.dedoimedo.com/computers/rpi4-ubuntu-mate-hw-video-acceleration.html to get some hw video acceleration but still when I try to play 4K mkv (HEVC 10bit) in vlc, it doesnt work, just black screen... 1080p seems to be quite ok...
Also in chromium/FF youtube is choppy, sometimes even on 360p (even tho I enabled the hw acceleration there too)
Does it work for others ok, or is there no way to fix it?
Because I also tried libreelec and it works fine there (4K mkv and the youtube app there too), so the HW should be able to handle it just fine
also loading/rendering pages in chromium and FF takes a while
I run the OS from Kingston 64GB micSDXC Canvas Select Plus 100R A1 C10
and it's on wifi, but the speed is getting to 50down/40up MiB/s, so loading should not be a problem, probably rendering
Playing video's on youtube up to 720P works fine here with 20.10 on the Pi 4 8GB. Above 720P it get's either stuck only sound playing or choppy.
And iirc hw video acceleration was enabled by default in the Ubuntu MATE 20.10 Pi image. https://ubuntu-mate.org/ports/raspberry-pi/
I'm running it from a SSD by the way and using a ethernetcable, no wifi.
I think it has to do with hardware acceleration possibly not being available in a Pi. I sold my RPi 4 around November so I don’t remember if I had screen tearing. Have you checked the Raspberry Pi website on this? They may have a more concrete answer,
I don't want to sound rude but most of the time i don't see leepspvideo as a reliable source given the mistakes he made in a couple of videos, which indicates he sometimes doesn't really know what he is talking about or what he is doing.
A example is the video showing RPI OS on which he installed the MATE desktop and says it's Linux Mint running on the Pi while it was just the MATE desktop on top of RPI OS. Another one is where he thinks there's a bug in Ubuntu Unity which wasn't a bug at all. Then there was one where he showed how to install Xfce and thought he was using it while in fact he was using Gnome 3. Etc..
If one is making such videos then they should at least have some knowledge and know what they are talking about. Just my 2 cents.
Ok, because I just put libreelec on the sd, when @Utsuro responded, I had to put back ubuntu mate (twice actually, cos first time it got corrupted and I couldnt load the partitions for some reason) and then set up all back again
but the h264ify works better than without, not great I'd say for 1080p, but maybe good enough
I'll just keep it that way and wait for what OSMC brings, when/if they (ever) release a version for RPi4