Rate-distortion analysis of nonlinear quantisers for video coders

Quantisation is used in video coders such as MPEG in association with rate control scheme to regulate the data rate of compressed video bit stream entering the transmission buffer. When the transmission data rate is limited the quantiser has a crucial effect on video data rate and video quality. The quantiser step size is generally determined by a linear non-adaptive method with respect to the buffer occupancy. In this paper, we investigate in the framework of rate-distortion theory two adaptive nonlinear quantiser control functions, sigmoidal and unimodal, which achieve superior video rate control performance while maintaining similar video quality to the linear case. Their performance for video rate fluctuation has also been analysed in both analytic and experimental ways.