Linear Real-time Rate Control

Abstract

Most existing rate control schemes in the literature calculated quantisation parameters of the macro-blocks (MB) based on the standard deviation of the residue before quantisation. We found that some factors after quantisation (eg probability of non-zero quantised coefficients, standard deviation of quantised coefficients, mean absolute difference of quantised coefficients (MAD’) divided by standard deviation before quantisation, Context-based Adaptive Variable Length Coding (CAVLC)) were new factors, having an interesting property that the rate tended to be linear with those factors. This work investigated the relationship of bit rate and distortion with MB quantisation step size and these factors. Then we established rate and distortion models with MB quantisation step size and these factors. By Lagrange optimisation, the distortion model was minimised subject to the target bit constraint, resulting in obtaining the closed-form formulas of optimal quantisation parameters. Interestingly, our proposed alg...