I found that
cpufreq scaling causes "slow" video playing.
From beginning is all ok, but after about 10 seconds cpu speed fall to on demand level
and after video start skipping some frames of movie. If mouse is moving speed can also grow up and after few seconds also fall.
When I try change
cpufreq to maximum speed all is OK, but I must use terminal command with
sudo cpufreq-set -r -d 2.6GHz -g performance
Have somebody solution for normal user?