A portion of the material in this chapter is based on research at AVA Media Systems. Section 2 contains contributions from earlier work with Tsuhan Chen, Carnegie Mellon University, Electrical Engineering Department. The Informedia material is based on work supported by the National Science Foundation (NSF) under Cooperative Agreement No. IRI-9817496. Christel and Wactlar are also supported in part by the advanced Research and Development Activity (ARDA) under contract number MDA908-00-C-0037. CNN and WQED Communications in Pittsburgh, PA supplied video to the Informedia library for sole use in research. Their video contributions as well as video from NASA, the U.S. Geological Survey and U.S. Bureau of Reclamation are gratefully acknowledged. More details about Informedia research and AVA Media Systems can be found at http://www.informedia.cs.cmu.edu/ and http://www.savasystems.com.