MPEG-4 constant-quality constant-bit-rate control algorithms

Abstract

Most constant bit-rate control algorithms aim to produce a bitstream that meets a certain bit-rate with the highest quality. Due to the non-stationary nature of the video sequence, the quality of the compressed sequence changes over time which is not desirable to end-users. In this paper, two constant-quality CBR control algorithms are proposed. They aim to produce CBR bitstream with the highest quality while having low variation in quality. Rather than controlling the quality indirectly as done in previously reported constant-quality control algorithms, they control the quality directly by using quality-matching algorithms. The frame-level Laplacian Constant Quality (FLCQ) algorithm allows one Quantization Parameter (QP) per frame, and uses a new rate-distortion model based on modeling DCT coefficients as having two-sided Laplacian distributions. The macroblock-level Viterbi Constant Quality (MVCQ) algorithm permits the QP to be changed for each macroblock using the Viterbi algorithm which reduces the search complexity. For both algorithms, besides the target bitrate, an extra degree of freedom is introduced that allows trading the variation in quality with the accuracy to the target bitrate. Simulation results show that the proposed algorithms outperform Q2 and TM5 by offering similar or higher PSNR while having lower PSNR variance.