Variable bit rate (VBR) video coding is emerging as a means to support full motion video services in broadband packet networks. In this paper, we use a motion adaptive VBR video codec and develop a motion-classified model to represent the characteristics of various classes of motion activities, including scene changes. The codec switches between interframe, motion compensated, and intraframe coding corresponding to low, medium, and high motions and scene changes, respectively. Our model captures the motion of various video scenes by providing the statistics of VBR-coded video traffic through a first-order autoregressive process with time-varying parameters. The parameters of this model are obtained from a VBR-coded sample video sequence with the objective of matching the bit-rate distribution and the autocorrelation among the bit rates. We evaluate the validity and accuracy of the model by comparing the bit-rate distribution, first through fourth-order bit-rate statistics, and the correlation coefficient among the bit rates of two successive frames of the video sample with those of the model. Using this model, we then present and discuss the characteristics of aggregated traffic sources.

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