Concatenate mp3s in a directory and subdirectories into a .m4b file

concat_mp3s_to_m4b.sh

# https://gist.github.com/alecjacobson/b4e8f59bbd251ed81df4c5fe8441f630
#
# brew install ffmpeg --with-fdk-aac
OLDPWD=$( pwd )
cd "$1"
paths=$( find . -name "*.mp3" | sed 's/\([0-9]\)/;\1/' | sort -n -t\; -k2,2 | tr -d ';') 
echo "$paths"
concat_paths=$( echo "$paths" | tr '\n' '|' )
ffmpeg -i "concat:$concat_paths" -c:a libfdk_aac -b:a 128k -f mp4 "$2"
cd "$OLDPWD"