When I watch this youtube video - http://www.youtube.com/watch?v=KqnB2Ew0SFM&feature=BFa&list=WL2AA75EB885F2A4B4 it's in flash.
But when I click on http://www.youtube.com/watch?v=LD3ywXEydyk - that video is in html5.
Why are some videos in flash and some in html5? Also how can I force html5 for videos (for example, when I want to use the speed-up feature)?