I. Introduction
H.263 is A low-bit rate video coding standard aimed at providing interactive video for Internet and mobile connections [1]. The compressed video bitstream obtained via H.263 and similar codecs presents some characteristics which are crucial for the efficient design of wireless mobile video systems. Among them are the variability of its rate, the uneven effect of degradations (errors or losses) on different parts of the stream, and the sensitivity to delay. The variable bit rate (VBR) nature of H.263 video is due to variations in content and coding mode from one video frame to another: frames with heavier motion will necessitate more bits, so as intracoded (I) frames as opposed to the intercoded (or predictive, P or PB) ones [1].