In YouTube’s case, that means that browsers that support the HTML5 tag and can play H.264-encoded video can now watch videos on the site without needing to use Flash at all. Since Flash is enough of a resource-hog on OS X that
entire software utilities to avoid it exist, this is a pretty compelling move for Mac users. On the Mac, only Safari and Chrome support the technologies needed for YouTube’s implementation—that means every (up-to-date) Mac user on the planet can start surfing YouTube Flash-free.
join the HTML5 beta with a single click, but YouTube notes that you’ll miss out on a few things if you do: for one thing, there are no ads (I know, terribly disappointing), but the beta also lacks fullscreen video, closed captioning, or annotations.
YouTube is calling the HTML5 beta an “experiment,” but in my testing it works flawlessly.