Constrained variable-bit-rate control algorithm for MPEG-2 encoder

The main objective of the variable bit rate (VBR) control for a video encoder is to maintain the picture quality during compression. Our constrained VBR control algorithm uses an external output buffer level to feedback the encoder. This algorithm predicts the next buffer level based on the current buffer level and the weighted average picture size of different picture types. The buffer level is fed back to the encoder and the quantizer scale is adjusted accordingly. If the buffer is near empty, the optimized quantizer scale is used. If the buffer is near full, the quantizer scale is increased aggressively to guarantee that the buffer does not overflow. This VBR encoder algorithm was implemented and compared with the CBR encoder algorithm. Several simulation results show that the VBR encoder provides better and more uniform picture quality than the CBR encoder at the same bit rate. For a desired picture quality, our VBR encoder can achieve more compression. If a network can support the VBR output, our constrained VBR control encoder performs better than the CBR control encoder.