A good reference that explains premultipled alphas well:
Premultiplied alphas
A good page on Y’CbCr:
http://www.mir.com/DMG/ycbcr.html
and the obligatory wiki page:
http://en.wikipedia.org/wiki/YCbCr
and how to use it with quicktime:
http://developer.apple.com/quicktime/icefloe/dispatch019.html
And a fun thought for the day:
