How to draw over video on a canvas element?

I'm trying to use a canvas for two things in my application. First is to display a video on canvas (which I already did). After that, I need to draw squares over this video, and it's in that part that I've got some trouble. When I try to use one canvas over another, the video always stays on top of the squares I'm creating. If i use only one canvas the same thing happens. Can someone help me please?