Accurate bit-rate and quality control for the MPEG video coder

The complexity of the MPEG video coding standard makes it a challenging task to provide simple strategies to tune the coder parameters in order to produce consistent quality images for a given bit budget. Pre-quantization and pre-coding of individual frames have been proposed in the literature as a viable solution to the problem. In this paper, we show that a simple statistical model for the DCT coefficients can be used to select quantization parameters at the macroblock level. In particular, 8 x 8 blocks of DCT coefficients are modelled as i.i.d. random vectors of independent variables. The rate-distortion performance associated to a given quantizer can be calculated from the model and the quantizer parameters can be locally controlled to meet the specified rate-distortion target. The experimental results show that, with a limited complexity, it is possible to achieve a great precision in the bit rate control without actual pre-coding.