If you're talking Youtube's HTML5 video player, I regularly stay below 20% CPU.  That's 10% total power, as percentages go above 100 when using more than one core.<p>Otherwise, it'd be Javascript + &#60;canvas&#62;, which so far is pretty darned fast, but not too friendly to ad-servers.  Not Flash-fast, but speedy, and quickly getting faster.  If JS+canvas gets more popular, you can bet that JS will get WAY more attention in this area.