This is an ancient filter, and we assume it's not useful anymore.
If you really want this, it's still available in libavfilter (e.g. via
--vf=lavfi=[pp...]). The disadvantage is that mpv doesn't pass through
QP information to libavfilter. (This was probably the reason vf_pp still
was part of mpv - it was slightly easier to pass QP internally.)
wm4
809936fdb9