Window-level rate control for smooth picture quality and smooth buffer occupancy

Traditionally, rate control consists of bit allocation and QP decision on R-QP model. In bit allocation, target bits is further confined if buffer overflows. Meanwhile, rate control should also give as smooth as possible picture quality. However, there is no explicit relationship between picture quality and encoding parameters, so the coding result on picture quality is usually unpredictable and uncontrollable. On the condition of smooth picture quality, the smooth buffer occupancy is preferable certainly. In our work, we first proposed a "window model" formulating the size of window and variations of picture quality and buffer occupancy. Thus, given the constraint on picture quality and buffer occupancy, the compliant coding result about them can be expected employing window model. Second, a window-level rate distortion (RD) model inspired by the traditional rho-domain model is introduced. Lastly, the evaluation of our proposal is presented with elaborate experiments.