Rechtstreeks vanuit Youtube?
https://www.google.nl/search?source=hp&ei=BWZ4W5PlMsHLwAK5qq-gCA&q=youtube+to+mp3&oq=youtube+to+&gs_l=psy-ab.3.0.0l10.3162.5980.0.7669.11.10.0.1.1.0.93.683.10.10.0….0…1c.1.64.psy-ab..0.11.696…0i131k1.0.ckUw8uNF3jE

Vanuit Firefox
https://addons.mozilla.org/nl/firefox/search/?q=youtube%20to%20mp3

Vanuit Chrome
https://chrome.google.com/webstore/search/youtube%20to%20mp3?hl=nl&_feature=free&_feature=4stars&_category=extensions