Replacing an Object with a Moving Object

I am replacing a moving object in a video with a second object that’s in another video.

In general it works ok, but because the second object is moving some in the second video, when I put that object in the first video I have to make some rotation and translation corrections in AE so that this second object lines up with the object being replaced.

Is it possible to stabilize the second object, so that it will be as if I am replacing the first object as you would with a still instead of a video (i.e. just using tracking data of the first object for the second 1 that is now still)?


If you can track the object you want to stabilize, then it may be possible.
The stabilize module will correct movement based on the area you track, so if you use “maximum smoothing” it should stay in one spot.
The only issue may be if the moving object has blur or organic rotation as this may look odd when stabilized in place.

Having a bit of trouble getting things to work. I tracked the second object. The clip in Mocha indeed has the object stabilized. But when I copy stabilization data and paste to either a null track or to the clip back in AE, the second object is no longer stabilized (even tho in Mocha it was).

Any idea what is going wrong? Is there rendering to be done in Mocha?


You might be pasting the data in at the wrong location, or pasting the data in on an object that isn’t the same size as the tracked composition. Mocha needs resolutions and frame rates to match. Have you checked out this tutorial? Boris FX | Align Surface and Mismatched Resolutions

Would timer-stretching the clip in AE cause an issue? That may be it.

Yes. That would do it.

Is there anything that can be done in AE on a layer that affects the tracking spline when Mocha is launched for that layer? Somehow when I open a layer in Mocha the tracking spline isn’t lining up quite right like it had been and I can’t figure out what the heck I did. The frame rate, frame size, and position I don’t think were altered.


They have to have been altered, or the frames must have been offset, OR the object you pasted or applied the data on wasn’t the same size as the comp.

I didn’t paste or apply data. This is just within Mocha. The spline is not quite on the object being tracked. What do you mean by the frames being off-set? None of the other possibilities seems applicable. Well, I’d swear size wasn’t altered, but I suppose that’s possible.

You can double check if you are unsure, check the Mocha file, and check BOTH the Footage interpretation and the composition settings, look for discrepancies in frame number, frame start, aspect ratio, size, and see if there’s any frame offset applied in the comp (sometimes things can get shifted on accident).

Try checking that and let me know,