!!!!!!!!!!!!!!!!!!!!!YOU HAVE TO HAVE 'MEDIAHUMAN YOUTUBE TO MP3' INSTALLED!!!!!!!!!!!!!!!!!!!!!

Get it here: https://www.mediahuman.com/youtube-to-mp3-converter/

This adds a 'DOWNLOAD MP3' button below the subscribe button on YouTube. Only tested with the new material design. Click on it and it will add the currently playing video to MediaHuman YouTube to MP3 download list.