Not efficient and only works in WebKit but -webkit-filter: blur(Npx) makes a nice effect
that will only blur an element, not the visible area underneath a translucent element. drpancake is referring to blurring the playing video is it scrolls underneath the title bar. this is pretty much impossible to do in HTML/CSS with moving content (video, gifs, etc), and only possible to do with static images by doing some very janky canvas hackery.
Caught us there. currently it is only an purple tinted overlay!