In AE, you can't apply a track to a mask shape. But sometimes, you really want to. In this example, I needed to get rid of a background light that showed up in a chromakey. Because of the nature of the key, using roto and paint were not precise enough because I had to work frame-by-frame. What I needed was to make one mask, and then track it to the movement of the subject.
Watch to find out how, or...
1. Precomp FG and BG
2. Track the movement of the subject in the precomp
3. Apply to a null
4. Create a black solid
5. Decrease opacity of solid so you can see through
6. Draw your initial mask on the black solid
7. Raise the opacity back to 100, set transfer mode to Silhouette Alpha, parent to null - now there's a hole
8. Precomp all of this
9. Reinsert your background behind the precomp to fill the hole
10. Adjust the mask shape as needed with keyframes
✏ Rotate around your subject - your axis of rotation should be around the subject in the photo.
✏ Choose subjects with little background detail to achieve the best Pixel Motion effect.
✏ Keep the motion between images very, very subtle. Practice rotating around your subject once or twice before you take the picture.
✏ Remember to have your camera on manual EVERYTHING: Aperture, Shutter, Focus, and White Balance. This will ensure the fastest multi-burst from your camera (DSLR or point-and-shoot). If you are shooting at a higher ISO, turn off in-camera noise reduction.
✏ Rename your files to numbers or alphabetical order - After Effects sometimes won't create a proper JPEG sequence with filenames such as "IMG_9738.JPG". In this example, I renamed my photos by chopping off the first 5 characters (making the filename "738.JPG") with a file renamer.
✏ Resize your images to your output WIDTH (1920 for my project). I created an action in Photoshop that automates everything. This will speed up your overall production and processing time.
☞ You can also use this method by zooming into your subject (instead of rotating) while shooting the images. Do this by either zooming with the lens, or physically stepping closer to your subject. Remember your manual focus here.
UPDATE: How to resize your photos/images:
✏ Download my Photoshop preset: http://bitly.com/resize-for-1080p-HD
✏ Follow the included instructions
REMEMBER that the photos you run through this Photoshop action WILL be overwritten. What I do is create a new folder called 'resized', copy my originals into it, then run the Photoshop action on the 'resized' images folder. After that, I chop off the first five characters of the filename with a file renamer such as File Renamer Basic (http://bit.ly/File-Renamer-Basic).