DaveTOR,
You're not alone. I've been able to replicate the problem myself. It's interesting that playback through XBMC (even using the Youtube add-on) is fine, while playback of the same content through a website is choppy.
I agree it seems to be between the video driver and the browser and/or browser plug in. It's not a hardware problem.
I've tested it under Windows 8.1 and Linux and see the same thing.
Jason
