feature-request: use new --video-crop for cropping operations

[dyphire]

Ref: mpv-player/mpv#12246
This will optimize performance and fix #19

Note that this does not bring hwdec support.

[Ashyni]

Hello,

I started to do some test with video-crop, every crop change looks smoother than lavfi-crop, i will implement it properly, your PR miss multiple stuff, thanks for your contribution anyway.

Has for #19, this issue is related to cropdetect filter chain and not crop, so it doesn't change anything.
And it's partially fixed with read_ahead_mode=0 (disable) in 7246723 and actually fully fixed with read_ahead_mode=1/2 (enable) by patch/ffmpeg/0001-avfilter-add-vf_dummysync.patch which need to be discussed with ffmpeg dev.

For now, the script remains limited to soft decoding or hwdec=*-copy.