After Effects script Tracker2Mask Tutorial
“Tracker2Mask computes the movement of maskshapes based on the movement of trackpoints. It is easy and flexible to use. In particular you don’t need one trackpoint for each maskpoint. In the tutorial I show how to rotoscope the shape of a moving car based on only four trackpoints, for simpler shapes often one trackpoint is sufficient.”
In the second Tutorial Mathias Möhl shows you some of new features like allowing local modifications of masks.
You can DOWNLOAD tracker2mask for free at (right click->save target as)