Motion Tracking Off Screen

[Darby Edelen]

Well, you inherently need something in the video to track, so there’s no way to use a feature outside the frame of the footage. But if you examine the help documentation on motion tracking you should find that you can have your track feature and your attach point in different locations (see the help if you’re not familiar with these terms).

This can cause problems if the feature doesn’t move at the same rate as the location you’re trying to attach to (due to parallax or other optical phenomenon), but if you can pull it off then it’s really one of the better options.

The only other option I’m aware of is animating the beginning and ending keyframes by hand or using an expression on the applied position data:

keyTime = position.key(1).time;
if(time > keyTime) loopOut("continue");
else loopIn("continue");

This will cause the layer’s position property to keep changing linearly based on the first known speed/direction and last known speed/direction. Since it’s linear it often doesn’t give great results, but it can be enough to fake the layer entering and exiting the screen.

Note: I didn’t get a chance to check that expression for syntax, if it causes problems let me know.

Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA

[Mike Clasby]

I don’t know if this is what you want, but if you want to move the the track points but leave the attach point in the same place (as the original attach point and tracking pointss move off screen), this might help:

Tracking obscured objects in video

https://studio.adobe.com/us/tips/tip.jsp?p=1&id=399&xml=aft6tracking

Here’s an excerpt:

5. Move the search and feature regions. When the tracked object becomes obscured so that the feature region can no longer track it, stop the analyzing process. If necessary, back up a few frames, and then move the feature and search regions to the new feature. Leave the attach point in the same location by pressing Alt (Windows) or Option (Mac OS) as you drag the area of the track point between the search and feature regions, or by dragging the edge of the feature region.

So can you just start tracking and move the track point just before it’s about to leave the screen (on the left), move it to the right while pressing Alt (Windows) or Option (Mac OS), if I’m reading correctly.

[Scott Roberts]

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