ok, Found this and know why,
https://forum.doom9.org/showthread.p...98#post1846298 (but don't know why
it's say 2 not 1 maybe because the video is yv12?)
maybe you can make it silently change u and v from 3 to 2 if it 0 (and ignore the Threshold if u and v not 3)
and still we have the avs 2.6 problem
https://i.imgur.com/xXtw5f0.png