Quickly want to convert a bunch of mp4 to mp3 (so you can listen to it whilst you run e.g.).

Here is a bash scrip that just does that.

#!/bin/bash
for fullfile in *.mp4; do
	filename=$(basename -- "$fullfile")
	extension="${filename##*.}"
	filename="${filename%.*}"
	#echo $fullfile
	#echo $extension
	#echo $filename
    ./ffmpeg.exe -i "$fullfile"  "$filename".mp3
done