In commit de6d57f0 libplacebo enabled drift compensation by default.
mpv already tracks error and adjust the speed by itself.
This commit fixes judder visible when slowing video a lot, ex. playing
back at 10% speed.
Set ideal vsync duration also when dropping frames, libplacebo estimate
currently own values anyway, will be useful later...
See: https://code.videolan.org/videolan/libplacebo/-/commit/de6d57f021e2336851f51b1a8538aa1484c56607