Detection of changes in surveillance videos

We provide theoretical and experimental results showing that the dimension of video trajectories is a useful tool to access the mid-level content of videos, such as the appearance or disappearance of an object, and changes in the velocity and direction of moving objects. Moreover, the amount of change is proportional to the size of the objects involved and their speed. All this is achieved by a robust technique of dimensionality computation of video trajectories based on eigenvalues.