Controls which field in the resized image the original image will be copied too.
When using avisynth's internal parity value top field first (tff) = 1 and bottom
field first (bff) = 0. Possible options:
-2 = alternates each frame, uses avisynth's internal parity value to start
-1 = uses avisynth's internal parity value
0 = bottom field
1 = top field
2 = alternates each frame, starts with bottom
3 = alternates each frame, starts with top