Wed Nov 18 13:37:10 CET 2009
To be pedantic, these are not the same:
Y luminance = detected energy
Y' luma = brightness = gamma-compressed luminance = electric voltage
However, in digital video, the Y is always gamma-compressed, and the
prime is often removed.
YPbPr is the analog equivalent. For more info see YUV(analog) 
and YCbCr(digital) .
How to make the video frame type as general as possible? Practically
though, only a couple of different formats are necessary.
These are the degrees of freedom:
* planar / packed
It seems that planar formats use only 2x2.
* component order
4:1:1 vertical + horizontal
Practically. Can the yuv format be made a subclass of the bytes
format? Not really, as it is not a growable buffer.