I tried to find anything related to my problem here but couldn't. I used search tool above, and found only one thread which mentions playing HD in YouTube, but I couldn't solve my problem.
And the problem is in the subject line - I can't seem to find a way to play HD videos in TOR browser. I don't say it's whonix problem because I can play HD videos in Iceweasel and Chromium. It's probably TOR related, but I tried in their forums and still couldn't find the answer. I can only play 360p videos.
So, I run Whonix GW and WS in KVM in a Linux host. If you need any additional info please let me know.