This is very cool. I built one of these myself around Christmas; Claude Code can put one together in just a couple prompts (this is also how I worked out how to have Claude test TUIs with tmux). What was striking about my finished product --- which is much less slick than this --- was how much of the heavy lifting was just working out which arguments to pass to ffmpeg.
It's surprisingly handy to have something like this hanging around; I just use mine to fix up screen caps.
Commenting mostly because when I did this I thought I was doing something very silly, and I'm glad I'm not completely crazy.
You can use AI to figure out the arguments to ffmpeg. But indeed it seems like there's just a single call to FFmpeg CLI to power the whole thing which is amazing.