How do you convert an entire directory with ffmpeg?

Question

How do you convert an entire directory/folder with ffmpeg via command line or with a batch script?

Answer 1

I needed all the videos to use the same codec for merging purposes
so this conversion is mp4 to mp4
it's in zsh but should easily be convertible to bash

for S (*.mp4) { ffmpeg -i $S -c:v libx264 -r 30  new$S }