[M4IF Technotes] Chrominance positions

[the_ether]

Are the positions of the chrominance pixels in fixed positions on the screen
or are they relative to the positions of VOPs.
That is to say, the normal description is
Y  Y  Y  Y  Y  Y
  c       c       c
Y  Y  Y  Y  Y  Y
ie one Cb and Cr per 4 Y pixels
However, what if the VOP sits at position (1,0)? I presume that we would now
have
Y  Y  Y  Y  Y  Y
      C     C
Y  Y  Y  Y  Y  Y
ie the C values would have to be re-calculated as they now relate to
different Y pixels.
So I assume  that the chrominance values move relative to the VOP. In other
words I cannot blindly calculate the YCbCr values for the whole screen. I
have to decide on the VOP positions before calculating Cb, Cr.
Is this correct?
Regards
graham