[megema]

Ok, I've changed every refresh rate's pixel size manually.

The next issue: lots of skipped frames. 1 in every ~5s. With wsnipex/vaapi I had dropped frames too.

Edit.: Just tried LibreELEC. It's playing videos smoothly. No skips, no drops. Unfortunately, it's not an option. I need Ubuntu.

Edit 2.: I've just solved this issue. After purging HWE Xorg and installing the original one, everything seems fine. Kernel remained the HWE one.