YouTube HTML5 in Safari

Is there any way to actually get YouTube to play back HTML5 in Safari? Every time a video loads, it plays for 2-3 seconds before it interrupts and tells me I need Flash (which I obviously don't since the video was playing back just fine in a native player).

I've tried

  • YouTube's own HTML5 trial
  • YouTube5
  • ClickToPlugin
  • Disable HTML5 on YouTube (alongside YouTube5)
  • FlashToHTML5
  • Adblock to block the Flash-required alert frame altogether

So far the only reliable method is to change my user agent string to iPad (which then blocks another subset of videos because in their infinite judgment they allowed video uploaders to prevent playback on mobile devices).

Has anyone had any luck with this?