Greasy Fork is available in English.
Adds a MP3 Download button next to the subscribe button, thanks to youtubeinmp3 for their simple download service (http://youtubeinmp3.com/api/). Based off magnus's youtube2mp3 code. Just used something different as it wont open another tab.
< Commentaires sur Youtube MP3 Download Button
HTTPS work around
I made it so the URL is replaced by the http protocol on page load, so no more manual protocol fixing.
https://greasyfork.org/en/scripts/11718-youtube-mp3-download-button-https