Distortion policy of buffer-constrained rate control for real-time VBR coders

With rate policy, we can achieve buffer-constrained rate control for variable bit rate coder. Since rate policy emphasizes the stability of the state of the buffer, we can loose the advantage of variable bit rate coders, i.e., a (nearly) constant quality/distortion. To overcome the difficulty, the distortion policy has been considered in this paper. Based on both the state of the buffer and the distortion, we can formulate the distortion policy. By choosing a proper weighting factor of the cost function in the distortion policy, the state of the buffer can be stable and/or the variation of the distortion sequence can be kept small. In addition, properties of the distortion policy have been obtained. We also consider switching and adaptive methods for the weighting factor to adjust time-varying characteristics of blocks of images. Using a JPEG-like image coder, distortion policy has been applied to buffer-constrained rate control.