In this Tutorial I describe how you use my After Effects script Tracker2Mask.jsx to assist rotoscoping.
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.