When I had the same issue, I solved it this way:

lvxVidRencodeAll () {
  for i in *; do ffmpeg -i "$i" -c:v libx265 "zz-$i" ; done
  pw-play /usr/share/sounds/freedesktop/stereo/complete.oga
  }
lvxVidResizeAll () {
  for i in *; do ffmpeg -i "$i" -filter:v scale=-2:720 -c:v libx265 "zz-$i" ; done
  pw-play /usr/share/sounds/freedesktop/stereo/complete.oga
  }

They’re both in a script that gets loaded by my .bashrc. Then I simply open the terminal, in a dir full of vids to perform one of those functions, and I run the command. No args. The first one converts the video to H265, the second one resizes it to 720p and converts it.

Why I’m sharing this: because odds are you won’t use ffmpeg for a lot of different stuff, only for the same things over and over. You don’t need an LLM for that, you need to spend some time deciding what you want to do, and then storing it for later in a script.