How to draw on a layer on a video?

So here is what I am trying to do.

I'm trying to trace the movements of a video using the paint tool, and when I'm done I don't want the video to show, only my brush stroke on a white background. It's for a project where we are required to track the movements of a conductor, so as to see if a pattern forms.  So far, I can track the movements just fine using paint, but I am unable to do it so that the video is gone and my stroke is on a white background. Any step by step help would be much appreciated.