brew install youtube-dl ffmpeg
youtube-dl -f best 'http://www.youtube.com/watch?v=P9pzm5b6FFY'
youtube-dl -i --extract-audio --audio-format m4a https://www.youtube.com/watch?v=kK2hpeqkYjA
youtube-dl -i --extract-audio --audio-format mp3 https://www.youtube.com/watch?v=kK2hpeqkYjA
youtube-dl -i --extract-audio --audio-format mp3 https://www.youtube.com/playlist?list=PLi1FCxGBD-x6HW2OD0534F-NWjKXY2pyo
ffmpeg -i foo.m4a -acodec libmp3lame -aq 2 bar.mp3
find . -type f -iname "*.webm" -exec bash -c 'FILE="$1"; ffmpeg -i "${FILE}" -vn -ab 128k -ar 44100 -y "${FILE%.webm}.mp3";' _ '{}' \;