It's Script Sunday, and today's script is so useful it made the cut and was included in the latest edition of After Effects Studio Techniques. TrackerViz was written by Charles Bordenave, the guy behind NABscripts (no apparent relation to the conference beginning this weekend), based on requests and ideas from artist Sean Kennedy. Here's an excerpt in which I describe it.
If you are having a difficult time getting an After Effects track to stick, there's an alternative to continually reworking a single track; several not-so-accurate tracks, averaged together, will often be more accurate than any alternative approach. The setup involved is a slight pain, however, which is where the script comes in; it automates the averaging process.
TrackerViz also lets you interchange tracked nulls and mask points, making it possible to effectively track in a mask (which is otherwise more or less impossible in After Effects). You first track a set of nulls, each with a unique name, corresponding to vertices on the shape. Select them in the order that you would draw them, and in TrackerViz choose and apply Layers to Shape in the Function menu. The result is not a shape layer but much more usefully, a solid with a keyframed mask applied to it. The mask can be used to replace any equivalent hand-drawn masks applied to layers.