avfilter/vf_scale: fix 4:1:0 interlaced chroma pos

The current logic hard-coded a check for v_sub == 1. We can extend this
logic slightly to cover the case of interlaced 4:1:0 (which has v_sub ==
2).

Here is a diagram explaining this scenario (with center-siting):

a   a   a   a   a   a   a   a

b   b   b   b   b   b   b   b
      X               X
a   a   a   a   a   a   a   a

b   b   b   b   b   b   b   b

a   a   a   a   a   a   a   a

b   b   b   b   b   b   b   b
      Y               Y
a   a   a   a   a   a   a   a

b   b   b   b   b   b   b   b

a = even luma rows
b = odd luma rows
X = even chroma sample
Y = odd chroma sample

In progressive mode, the chroma samples sit at (384, 384) respectively.

Relative to the 8x4 grid of even luma samples (a), the X sample sits at:
  h_chr_pos = 384
  v_chr_pos = 192

Relative to the 8x4 grid of odd luma samples (b), the Y sample sits at:
  h_chr_pos = 384
  v_chr_pos = 576

The new code calculates the correct values in all circumstances.

0 files changed, 0 insertions, 0 deletions