Now, I mentioned I did not have a shot without the motorcycle in it. To get around this issue, I exported a frame with the motorcycle right in the middle from the video and removed the bike manually in Photoshop. Ideally, you'd want to have a photo or a video of the scene without the vehicle you want to blow up, called a clean plate, and you want to capture that clean plate at the same time you're filming your actual scene. It took a little bit of work, but here is the clean plate I created:
Add the the clean plate into your composition as a new layer.
Trim it down to start exactly when you want the explosion to tear the motorcycle apart.
If we scrub through the footage, the motorcycle disappears, but the moment the clean plate becomes visible, the video seems to freeze. This is expected as the clean plate layer is just covering everything underneath it up.
What we need to do is position the clean plate layer properly in our 3D scene, right in front of the motorcycle.
For this, turn the layer into a 3D layer and reveal the position property on it.
Also reveal the position property on the camera and copy the current position of the camera across to the position of the clean plate. Since the camera is animated, I am doing this manually for the x, y and z coordinate.
Next, reveal the orientation property on the cover up layer and the camera and copy it from the camera to the cover up layer. Again, I am doing this one value at a time to make sure I'm not screwing anything up.
If you now go to the top view, you should see the clean plate layer and the camera at the exact same position.
Quite a bit in front of the camera, we can see the Motorcycle Marker null object we created. We now want to move our clean plate forward to just before the marker for the motorcycle. This will place the layer in 3D space at the position of the motorcycle.
Return to your active camera view and scale the cover up layer to fit exactly over your composition.
The layer should hide the motorcycle perfectly if you enable/disable it. Lower the opacity of the layer, and then draw a rough mask around the motorcycle. Here is a screenshot of the clean plate overlayed onto the motorcycle.
I am going to give the mask some feathering to blend it in a bit nicer. If we bring the opacity back to 100%, the motorcycle should be fully hidden and scrubbing through the footage, the motorcycle should disappear from the moving shot.
Now this is not perfect because the clean plate layer is just a flat layer standing at the same position as the motorcycle and as the camera moves, it starts to mis-align with the background elements, especially the pillars.
We can fix this up to some degree by animating the position of the clean plate to better match the elements it is covering up.
I am also going to expand the mask a little to ensure the motorcycle remains fully covered. Still not perfect, but for our purposes this should be sufficient.
Let's start destroying the motorcycle!