HTML5 brings native multimedia to browsers. In ye olde days, video and audio were handed off to third-party plug-ins (which may not be available for every device or operating system). Communication between a browser and a plug-in is limited and therefore the multimedia was very much a black box.
Then along came HTML5. All the major browsers support native video and audio (including Internet Explorer), albeit with the need to double-encode your media because IE and Safari support only royalty-encumbered codecs.
Suddenly, video can be styled with CSS – you can overlay semi-transparent videos over each other, set borders and background images, rotate them on hover with transitions and transforms and all kinds of other wonders.
Via Nicolas Weil, digitalassetman