I compared the two methods of interpolation - bilinear and Lanczos (see the pictures below).
The first frame was resized to 1920x540 by VerticalReduceBy2(Left) - left eye only, and restored to 1920x1080 by built-in DXVA decoder with Daum PotPlayer.
The second frame was resized to 1920x540 by Lanczos4Resize(Left, 1920, 540) - left eye only, and restored to 1920x1080 by built-in DXVA decoder with Daum PotPlayer.
It has a little differences, but I can not choose that is better.
Perhaps for size reduction by 2 in one axis interpolation method does not important, because it has a insignificant differences.
I'll compare again later with brighter, more detailed and grainy video.
bilinear:
Lanczos:
bilinear:
Lanczos: