[MPlayer-dev-eng] Help with MMX asm code

[Billy Biggs]

Jason Tackaberry (tack at auc.ca):

> On Thu, 2003-10-23 at 10:19, Billy Biggs wrote:
> >   Actually even worse, that means you have only one alpha value for
> > every two pixels ?  That does not seem right at all.
> 
> No, it's one alpha value for every pixel.  Is 4:2:2:4 incorrect
> notation for that?

  A 4:2:2 signal has chroma samples for every second pixel.  Usually you
have this in memory as a packed format like this:

  [Y'][Cb][Y'][Cr]

  So that is for two pixels, the Cb/Cr samples correspond to the Y'
sample on the left, and the Y' sample on the right has no associated
chroma samples, they are interpolated.

  So when you say 4:2:2:4 I sort of assume you've got something like
this in memory:

  [Y'][Cb][Y'][Cr][A]

  Where we have one alpha sample but two luma samples.  Please describe
your memory layout better and maybe it will make more sense to me :)

  -Billy