Why does this motion tracked rig not render correctly?

I just tried to make a very simple example of camera tracking, and I’ve got most of it working, but when I try and render, it doesn’t show the 3D view cube, but it only shows the video clip. I’ve tried deleting the clip, but that makes it render a blank screen… I’ve made sure everything is set to renderable, there is light, and when you go into the 3D view and view it rendered the cube shows up! I might be missing something with the compositing or something? I’m completely out of ideas. Maybe I’m missing something simple, or maybe I completely screwed something up

untitled.blend (753 KB)