Fire up Cinema 4D and create a brand new project. Before doing anything else, open up the project settings and make sure they match your After Effects composition. My footage was shot at 1080p with 30 FPS.
Which format you use to export your rendered elements is up to you. Just make sure that you have the Alpha Channel option enabled so the footage does not end up being pre-matted. I have chosen to output my rendered debris elements as a PNG image sequence.
To make it easier for us to match up the 3D elements we will be creating with our After Effects composition, let's first set up our viewport background to display a frame from our clip. Create a new Background element in Cinema 4D.
Go to the material toolbar and select Create -> New Material.
Finally, select the new material and go to your Object Inspector. I have exported a single frame of the roof destruction composition from After Effects as an image at 1920 x 1080 resolution. Select this scene background image as the material texture.
Now drag the new material onto the Background object we created earlier.
Your viewport background will now show the exact same scene as your After Effects composition.
Now we're ready to roll and start adding 3D elements into this scene!