# convert files in directory from m4a to mp3
function m4a() {
find . -iname '*.m4a' -exec bash -c 'ffmpeg -i "$1" "${1/m4a/mp3}"' -- {} \;
}
use Run Shell Script (bash / pass in as arguments)
for f in "$@"
do
if [[ $f == *.m4a ]]
then
/usr/local/bin/ffmpeg -i "$f" "${f/m4a/mp3}"
fi
done