For the life of me I can't figure out how to move around Cinema 4D without affecting the camera. I thought that if held ALT and moved around then you would just be changing your view and not actually move the camera. So I've done all this work in Cinema 4D and then I moved my camera somehow and I can't align it with my plate (footage background) anymore.
There's a little icon on the Camera in the Object Manager next to the "traffic lights" that control editor and renderer visibility. It looks like a dot in the middle of a rectangle. When it's white, the camera is active. When it's active, your viewport navigation affects the camera. Click this icon to toggle the camera on and off.
Viewport navigation has a separate history stack, and normal Undo does not work on viewport navigation. If you accidentally move in the viewport, you can press Ctrl+Shift+Z to undo.
option#2: add (at least) one keyframe to your camera, and make shure that 'autokeying' is turned off. When you have moved it, stepping through te timeline will have it snap back to it's keyframed position.
option#3: add a 'protect'-tag to your camera, now it can't move at all.