Scaling a video with mpv is very easy, this command line is written in the console. Press ` to open the console and then type this command. This will either downscale a 4K video or upscale a lower res one.
set vf format:w=1920:h=1080:convert=yes |
This is a very useful way to scale a movie to a desired size whilst watching.
This version of the downscaling function is more efficient on older machines.
dscale=catmull_rom |
This entry written in the ~/.config/mpv/mpv.conf file will allow the same scaling via the CPU.
sws-allow-zimg=yes zimg-fast=no zimg-scaler=bicubic zimg-scaler-param-a=0 zimg-scaler-param-b=0.5 zimg-dither=no |
Press I when playing a movie in mpv to see information about the video file.

This is very comprehensive information. Press Shift-I to display statistics until pressed again. Press Shift-Control-Backspace to save your position in the movie. Then press Shift-Backspace to revert back to that position in the movie. This would be great for seeking around in a movie and then reverting back to the previous position. < and > will seek backward and forward in a playlist.
Another way to scale video using mpv. Use the command line.
Many thanks for this entry about Mpv scaling.
I have a question though, when you write :
“This entry written in the ~/.config/mpv/mpv.conf file will allow the same scaling via the CPU.”
Does this mean it will upscale/downscale automatically all the video or is there a command line argument to use in conjunction?
All videos.