Follow these steps to use a youtube video as your background music.
1) First of all: go to youtube and choose a video.
2) Click the "Share" button under the video > click "Embed" > Copy this embed code
(It won't work if you are not allowed to embed the video)
3) Now we have to hide the video > Set the width and the height to "0".
4) We want the music to start automatically > add &autoplay=1 after the youtube link.
5) Go to the page where you want the music > drag a "embed code" element on the page (bottom of the page) > paste the embed code in it