all youtube videos are playable in html5
every single video is available as mp4.
I don't use flash for security reasons.
If you use internet explorer 10 in windows7 without flash you will notice all videos play flawlessly
in ubuntu with firefox or chromium you will notice some videos will complain about not being able to play without flash
e.g.
https://www.youtube.com/watch?v=xXIcQaNiy0g
now observe how easily we can make it play without flash:
https://www.youtube.com/embed/xXIcQaNiy0g
it has nothing to do with flash but everything to do with ads and youtube partners and monetization and google shenanigans
in your channel settings turn off ads and monetization etc etc and your channel will be 100% html5:
https://www.youtube.com/user/nomenkultur
I haven't used flash in over a year now and everything in my youtube works fine
also in case you didn't know
https://www.youtube.com/tv#/browse