Constant Quality Video Encoding Based On Rate-Distortion Functions

Over the past few decades, digital video compression technique was extensively used in video communication, TV broadcast, video on demand, and digital storage. Several international industry standards have been established, including MPEG-1/2/4, H.263 and H.264. The newest H.264/AVC and AVS video coding standards doubled the coding efficiency relative to the performance of prior standards such as MPEG-2.For all video encoders, rate control plays an important role. It directly affects the bit rate and quality of the output bit streams. So it is very important for us to have an in-depth study on the key techniques used in rate control and improve the coding efficiency of the new coding schemes. In this paper, we present a two-pass variable bit rate (VBR) coding algorithm for H.264/AVC, using a novel R-D model. The model is developed based on the statistical analysis of the integer transform coefficients with generalized Gaussian distributions (GGD). Also, we develop a new VBR bit allocation method for MPEG-2/AVS video transcoding. The main contributions in this paper are listed as follows:1. Rate-distortion analysis and modeling of the H.264/AVC standardIn this paper, we first present a new rate-distortion model for H.264. This model is developed from the statistical analysis of integer transform coefficients using GGD. The analysis and modeling are based on information theory and the quantization scheme of H.264.2. A novel Two-pass VBR bit allocation algorithm for H.264/AVC standardIn this paper an effective VBR algorithm for H.264/AVC is developed, which adopts two-pass encoding to achieve a constant video quality. Characteristics of the entire video sequence are collected and analyzed in the first pass, using our new R-D model, and then the sequence could be optimally re-encoded in the second pass. Experimental results show that the proposed algorithm is effective and efficient to reduce the PSNR variation and provide consistent visual quality.3. A new rate control method for MPEG-2/AVS transcodingIn this paper, a simple and effective rate control method for MPEG-2/AVS transcoding is presented. First, the initial quantization parameter of the transcoding is achieved by a new R-D model in transcoding. Then, during the AVS encoding, quantization parameter is adjusted according to the MPEG-2 bit rate using our new rate control algorithm. Experimental results show that the proposed algorithm can effectively reduce the PSNR variation and provide consistent visual quality.