What is difference between in and on option at perspective filter.
in
Input frame count.
on
Output frame count.
Two commands same preview.
ffplay -f lavfi testsrc2 -vf perspective=print(in):0:W:0:0:H:W:H:0:0:0:eval=frame
ffplay -f lavfi testsrc2 -vf perspective=print(on):0:W:0:0:H:W:H:0:0:0:eval=frame