This ducks the real issue.

I'm not all that concerned about the efficiency of the codec and of the mechanism that flushes video to the screen. That said, <video> in a web browser that's codesigned to work on a platform is always going to give a complex cross-platform app like Flash a run for the money.

I'm more concerned that Flash burns up CPU for no reason at all. I mean, my Mac Mini hits 100% CPU and sounds like a helicopter taking off when I've got a little tiny flash ad open on any tab. I got no trouble w/ internet ads, but it's ridiculous that one stupid ad should be able to completely disable the power management system on my computer.