if your unlucky enough to NOT have a computer, than this will help i hope.
You need to be able to run flash lite for this to work.
http://www.video2mp3.net/index.php
this website is wonderful for converting to mp3. The next website is for downloading youtube videos to mp4.
if like me youtube redirects you to the mobile version. then scroll to the bottom click desktop. bookmark the video and then copy the saved bookmark link into the space that says "paste link here" or something similar. let me know how it works out cheers