I. Introduction
Video communication is becoming an increasingly important part of the global information infrastructure. Unlike text or image, video communication requires huge volumes of data being transmitted in a timely manner, so highly efficient compression must be used. Extensive research in both academia and industry has resulted in a large number of standards in the past decade, such as H.261 [1], H.263 [2], H.263+ [3], MPEG-1 [4], MPEG-2 [5], MPEG-4 [6], etc.