FlashToHTML5 is a great Safari extension that will attempt to load all YouTube Flash videos as HTML5 at the highest possible resolution, helping you to maintain a Flash-free Mac OS Xinstallation and thus giving portable Macs more battery life by reducing CPU usage.
FlashToHTML5 plugin is a free download from the developers site
The extension serves the same purpose as the manual HTML5 experimental setting in YouTubes preferences, but if you don’t have a YouTube login then you can’t force HTML5 video anyway.
If you do have to use Flash for other reasons, it’s highly recommended to install a ClickToFlash plugin for Safari or enabling the included click-to-load Flash feature in Chrome, both offer the same benefits that prevent CPU hogging Flash video from automatically loading in the browser.
