We found out this cool website: Yout.com that offers you the possibility to download a YouTube audio or video to your computer in very simple steps. To be honest, it cannot get any easier than this. Check the animated GIF below as they explain it on their own website.
Although you can paste the whole URL directly on the Yout.com page, I think the easiest is to do it directly form the YouTube page, just trimp the domain YouTube.com… to YouT.com and press enter (leave the rest of the original YouTube URL) and you will see the buttons to download in MP3 or MP4 format.
How you can use the MP3’s or MP4’s you download probably is ruled by the rights each media has so you might want to check on the YouTube description area of the file you download.