http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwmt/html/yuvformats.asp

YUV:  Y = Luma, U = Chroma B, V = Chroma R

Chroma channels have a lower sampling rate than the Y channel.
4:2:2 = 2:1 horizontal downsampling, zero vertical.  Every scan line contains four Y samples for every two U or V samples.
4:2:0 = 2:1 horiz, 2:1 vert
4:0:0 = ?

Origin: upper left

4:2:2:
 byte 1 = first y sample
 byte 2 = first U(Cb) sample
 byte 3 = second Y sample
 byte 4 = first V(Cr) sample