Indexing key positions between multiple videos

Given two or more video sequences containing similar human activities (running, jumping, etc.), we want to devise a method which extracts spatio-temporal signatures associated with these activities, compares these signatures, and aligns key positions from different videos. We introduce a method which, in conjunction with a number of hypotheses, allows the analysis of the motion of specific body parts and extracts their 2D (image plane) time-varying trajectories as well as their 3D trajectories. Two such trajectories recovered from two different videos have different characteristics. We develop a curve registration technique which consists of estimating a transformation which maps one time-basis (of the first curve) onto another time-basis (the second curve). We also analyse in depth the conditions under which such curve registration techniques are valid. Finally, we show results with two similar athletic events performed by two different athletes.