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Abstract

The effective (or logical) size of the encoder buffer in a video transmission system is varied with the transmission bit-rate. Also, a minimum fill level is maintained in the encoder buffer whenever the transmission rate is too high to assure otherwise that the decoder buffer will not overflow or underflow. The encoding rate is varied so as to maintain a fill level in the encoder buffer within limits. In the preferred embodiment, the logical encoder buffer has a size which is maintained at R.DELTA.T(1-m.sub.1)-M, where R is the average transmission bit-rate, which may vary, .DELTA.T is the fixed delay between the encoding and decoding processes for a transmitted video signal, R(1-m.sub.m) is the minimum instantaneous transmission rate that the communication system achieves at average rate R, and M is the maximum total buffer storage in the communication system. When the decoder buffer has a size less than R.DELTA.T(1+m.sub.2), where R(1+m.sub.2) is the maximum instantaneous transmission rate at average rate R, the encoder buffer fill level is maintained above a minimum level that is equal to the amount by which the decoder buffer is less than R.DELTA.T(1+m.sub.2).

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