[Mark Spraker]

If it’s on a black background you could try using a Difference Matte. Just throw a Black Solid under the footage layer and use that as the Difference Layer.

It’ll need some fine tuning, sure, but it’s a start.

[Mark Spraker]

https://library.creativecow.net/articles/kramer_andrew/Set_Extensions.php

I believe that is the tutorial he was talking about.

———-

Here is the gist of how I would approach this:

Shoot the scene with as little camera movement as possible. Panning is ok, just don’t over do it. All that matters is that you can get a good 2D track in AE.

Once you’ve got the footage, save a still frame where you can see all of the buildings and use Photoshop (or whatever image editing tool you have) to create the destroyed look. You can do this inside of AE if you don’t have PS but it’s more work.

After that, it’s just a matter of motion tracking each building with the appropriate “destroyed” bits. It’ll be more involved than just a simple Sky Replacement due to parallax. It should definitely be possible nonetheless; Just keep it simple.

[Mark Spraker]

If you want to open a pre-comp as a footage layer for motion tracking (For example), you can right click on it and select “Open Layer” as mentioned before. Another option is to simply Alt + Double click on it.