Abstract

We present and compare methods for choosing motion vectors for motion-compensated video coding. Our primary focus is on videophone and videoconferencing applications, where very low bit rates are necessary, where motion is usually limited, and where frames must be coded in the order they are generated. We provide evidence, using established benchmark videos typical of these applications, that choosing motion vectors explicitly to minimize rate, subject to implicit constraints on distortion, yields better rate-distortion tradeoffs than minimizing notions of prediction error. Minimizing a linear combination of rate and distortion results in further rate-distortion improvements. Using a heuristic function of the prediction error and the motion vector codelength results in compression performance comparable to the more computationally intensive coders while running much faster. We incorporate these ideas into coders that operate within the p x 64 standard.