We will composite the UFO we rendered in 3dsMax back onto the original clip that we extracted the camera data from using Adobe After Effects. It won't fit onto any other footage because the camera used for the UFO is unique to this scene.
When importing your rendered UFO into Adobe After Effects (select the first EXR image and enable the 'Sequence' checkbox), there are a few things we need to set up to ensure the footage will match your composition. For this, right click the imported UFO sequence and go to 'Interpret Footage'.
Ensure that the frame rate matches the frame rate of your composition. You also want to make sure you enable the 'Preserve RGB' option in the Color Management tab.
Once you have placed the UFO on top of your base footage you will notice that it sits on top of all the branches in the scene. Of course, we want it to sit behind these branches. For this, you can duplicate your base footage, move it above the UFO layer and apply a Linear Color Key effect to key out the bright sky areas. You may have to tweak this a bit to suit your scene as your sky might be a different colour.
In the above screenshot you can see a bright blue outline around all the leaves. This happens because the bright sky bled into the colour of the leaves. This can be tricky to fix up cleanly. One tool I like to use in Adobe After Effects is the Keylight effect in After Effects to remove some of these ugly artefacts. It might not be perfect, but it will make the overlaying branches sit a lot more natural on the UFO layer.
Now let's look at how to create some awesome smoke and fire for our UFO!