BIT-RATE CONTROL FOR HYBRID DPCM/DCT VIDEO CODEC

This paper presents a simple approach to regulating the bit stream generated by the hybrid DPCM/DCT video codec so that the compressed hit stream at a variable rate can be transmitted over a fixed rate channel. Bit rate regulation is accomplished by appropriately quantizing the DCT coefficients where the quantization stepsize is obtained by multiplying a fixed weighting matrix by a scaling factor. For each frame, a single quantization scaling factor is determined by iteratively comparing the output bit rate with a target bit rate which is based upon the desirable bit rate, frame code mode, frame complexity and scene changes. The iterative comparison guarantees a quantization scaling factor which results in a minimum accumulated bit rate difference from the target bit rate for each frame. The simulation results demonstrate that the fluctuation of the output bit rate can be kept within a narrow margin while maintaining the quality of the reconstructed frames at a relatively stable level.