Constraints on the encoded bit rate of a video signal that are imposed by a channel and encoder and decoder buffers are considered. Conditions that ensure that the video encoder and decoder buffers do not overflow or underflow when the channel can transmit a variable bit rate are presented. Using these conditions and a commonly proposed network-user contract, the effect of a (BISDN) network policing function on the allowable variability in the encoded video bit rate is examined. It is shown how these ideas might be implemented in a system that controls both the encoded and transmitted bit rates. The performance of video that has been encoded using the derived constraints for the leaky bucket channel is presented.
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