reference materialFour point motion tracking in After Effects

Fall 2006ss

by Brian Mehrens

This is a tutorial on four point motion tracking in After Effects. This process is commonly used to put planar elements on live and moving objects such a replacing an image on a billboard as in the examples below. The movie on the left shows a plane with no element tracked to it. The movie on the right shows the same plane with an image tracked on the plane's surface.
Files used for this tutorial: image.psd TrackMe.mov TrackTutorial.aep 1.Begin a new project in AfterEffects. 2.Import footage that you are going to track. Here I am using TrackMe.mov (Image 1)	Image 1
3. Create a new Composition and drag the video into that Comp. (Image 2)	Image 2
4. Here we see our video that we are going to track. It is important to have an image with high contrast around the points that are going to be tracked. Here I have made some X markers to be used as tracking points. (Image 3)	Image 3
5. Now with the video layer selected go to Animation->Track Motion. (Image 4)	Image 4
6. In the Tracker Controls panel we see several options. The imortant one to look at now is Motion Source. This should be the name of the video that you are going to track. (Image 5)	Image 5
7. The next important thing to look at is the Track Type. Here because we are following a plane which has perspective chage we need to chage the option to Perspective Corner Pin. (Image 6)	Image 6
8. Now in our composition window we see our video with four tracking points. (Image 7)	Image 7
9. Click on the inner most square on one of the four corners and drag until the small x in close to a high contrast part of the image, in this case near the center of the X. (Image 8).	Image 8
10. Do the same for the other three square tracking points. (Image 9)	Image 9
11. Now with the timeline marker at the beginning of where you want to start tracking the motion press the Analyze forward key, it looks like a play button on the Tracker Controls Panel. (Image 10)	Image 10
12. The video will begin to play and the keyframes will be made for each tracker. When you reach the end of the video that you want to track, press the stop button. (Image 11)	Image 11
13. Now we see that the video has all these keyframes as a result from the track. (Image 12)	Image 12
14. Also on the timeline, we see the corresponding keyframes created for the tracker. (Image 13)
Image 13
15. Now load the image you want to have the track move. Here I have used image.psd. Load this image into the composition. (Image 14 and 15) Image 15	Image 14
16. Now select the video again. (Image 16)	Image 16
17. You will have to select the motion source again which is your video. (Image 17)	Image 17
18. Now press the Edit Targe button. (Image 18)	Image 18
19. In the Motion Target box select the layer of the image or video that you want to affect witht the motion tracking data. Here it is the image.psd image layer. Click Ok (Image 19)	Image 19
20. Now click the Apply button to apply the tracking data to our image. (Image 20)	Image 20
21. Now we see that keyframes are added to the image. (Image 21)
Image 21
22. Hide the video layer that you tracked or move it to the bottom of the timeline so that you image layer is on top. Now you can see the result. (Image 22) 23. Playback you video and the image should now match perfectly the movement of the video. Note: If the track wasn't perfect you may have to go in by hand and fix a few frames changing the Corner Pin attributes on specific keyframes.	Image 22

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