1.Go to youtube.com
2.Find / search the video or music that you want.
3.Get the code.Click the EMBED button just under the video player.
4.Now to autoplay it, add ?autoplay=1 in the code.
<iframe title="YouTube video player" width="200" height="27" src="http://www.youtube.com/embed/YG8XUIl6Z-0?autoplay=1" frameborder="0" allowfullscreen></iframe>
5.To hide it set the width and height into 1.like this:
<iframe title="YouTube video player" width="1" height="1" src="http://www.youtube.com/embed/YG8XUIl6Z-0?autoplay=1" frameborder="0" allowfullscreen></iframe>
6.If you dont want it hidden you can play around with the width and height^^
7.Paste the code either in the description or html body.