>> You can also try without HTML5 video setting on.

> Yes it works without html5

No, it doesn't. Even with Youtube's HTML5 video setting off, Youtube sends its videos to OWB via HTML5, at least as long as you have the Flash plugin disabled. And with the Youtube scripts in use, the calculated video URL gets embedded into HTML5 on the fly. Put simply, OWB cannot play Youtube videos in any other way than via HTML5.