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How to center on a tracked object?

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Charles Ka
How to center on a tracked object?
on Mar 23, 2018 at 10:21:31 pm

Hello all!

I'm fairly new to After Effects as well as any advanced video editing (I've always just faded in/out video/audio along with spotchecking/fixing audio. That's as far as I've gone.)

Now, my issue is that I want to have a tracked bit in my footage and center my frame around that footage while everything else around it moves essentially.


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Steve Bentley
Re: How to center on a tracked object?
on Mar 23, 2018 at 10:57:47 pm

So if a bouncing ball was in your shot you would want that ball to stay still while everything else moved? (and that's ok, i'm just trying to determine what you are after.)

Depending on the version of AE you have there are a number of approaches but the principle is still the same. Generally this is called stabilization. Find a detail that you can "track" and then tell AE to fix that detail to one point.

Instead of sending your tracking data to the position attribute of the footage you want stabilize you send the tracking data to the anchor point (it acts as an inverse movement) So if the ball goes up in the frame, sending "up" data to the anchor point makes the footage come down thereby keeping the ball where it was. We'll often send the data to a solid the same size as the footage and that way it's saved and not part of the footage at all. Then we can copy and paste that data anywhere you like or make an expression that links to the data to another piece of footage or run the smoother on the data before you paste it back onto the original it came from.

You can copy position data to the anchor point and visa versa but you can't copy rotation data to the position data or visa versa. Its all about how many elements the data has - position has x and y, so two elements, but rotation only has degrees - so one element.

I mention rotation because you can choose to turn on the rotation tracker as well so that the position stays still but so does the angle. There is no anchor point for angle in the same sense as "position". If you choose Stabilize in the tracker, this will be managed for you. But if you just want to play with the data, you often have to do a bit of 360-rotTrackData math to get the right data to paste back onto the rotation attribute. (you have to calculate your own rotation "anchor point".)

Be forewarned though - stabilizing can make your footage seem too small to fit your frame and you end up having to blow up the footage so you don't see the edges. That will make the footage softer. Move footage even one pixel and you can suddenly see an edge.



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Charles Ka
Re: How to center on a tracked object?
on Mar 23, 2018 at 11:24:33 pm

Yeah!! I definitely had a feeling that I had to inverse SOMETHING in the end... Thank you VERY MUCH for that in depth answer!!

I ended up creating a null, parented my initial footage to that, applied my tracking data to the position of the null, and copied the tracking data to my anchor of the initial footage (that's the child of the null).

Many many thanks! I think the footage I took wasn't all that great considering how it was of in a videogame engine and I need to get a better capture of it, but I think I "mastered" what I wanted to do.


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