yuv 4:2:0 - save some more common factors
yuv 4:2:0 - save some more common factors

shaves another ms/frame off of drawing on iPod Touch

chrislearn/ogv.js,chrislearn/ogv.js,paladox/ogv.js,chrislearn/ogv.js,chrislearn/ogv.js,xzf158/ogv.js,chrislearn/ogv.js,paladox/ogv.js,paladox/ogv.js,xzf158/ogv.js,paladox/ogv.js,xzf158/ogv.js,xzf158/ogv.js,xzf158/ogv.js,paladox/ogv.js