An object in a video clip should be tracked to move a mask across the screen, revealing a 3D object (extruded text). Imagine a shot of a sheet of paper on a desktop. The paper is pulled out of the view sideways, revealing the rendered object which appears to be on top of the desk.
So I imagine I need to composite the video in the background, and an animated mask on top of the text, so that the visibility of the text (= opacity of the mask) is zero where the paper is in the video, hiding it.
What I have: a video clip in the Timeline, an extruded text in the Scene, and two nodes "Render Layers -> Composite" in the Compositing Editor. When Rendering, the result shows only the video, but not the object.
I'd be happy with a short outline of the easiest steps I need to take to achieve what I want. But a few pointers to the tools I need to use or a rephrasing of what I am trying to do in the proper terminology would help in searching the information on my own. Motion tracking is not really necessary since it is a short clip and I'd gladly learn how to animate the mask manually.
I am using Blender 2.78a on Windows.