There are many tutorials and stuff showing how to extract multiple screenshots from a video using ffmpeg. You set -r and you can even start a certain amount in.

But I just want 1 screenshot at, say 01:23:45 in. Or 1 screenshot at 86% in.

This is all possible with ffmpegthumbnailer but it's another dependency I don't want to depend on. I want to be able to do it with ffmpeg.