Complexity, Rate Control And Quality Assessment In H.264

H.264/AVC video coding standard is provided formally by JVT (Joint Video Team) in March 2003, and it will be the second successful video compression standard after the MPEG-2/H.262 in future. The standard is designed to give a new technical solution to a broad range of applications, such as very low bit rate conversational services and entertainment quality broadcast, interactive video-on-demand services etc. So this standard obtains much attention from academic and industrial fields.Several important issues for real-time video coding have been addressed in this paper. They are the analysis and regulation of the coding complexity, applicable rate control and video quality assessment.Firstly, H.264 standard adopts many new tools to enhance the coding efficiencies, which are multiple reference pictures, variable block-size with seven block sizes in motion prediction, quarter-pixel accuracy for motion vector, short word-length integer transform, context-adaptive entropy coding and loop filter for deblocking. This paper analyzes the impact of every coding tool and parameter to the encoder in detail and the dependency within these tools. Then a method of efficiently and reasonably setting encoding parameters is brought forward at the balance of complexity and performance.Secondly, the mechanism and information source model is described. Cosidering the character of H.264 bit stream, we adopt a log-model and present a layered rate control algorithm. It includes the rate control of GOP layer, frame layer and basic unit layer. PSNR and subjective quality of the decoded pictures is improved and the actual bit rate is more close to the target bit rate. Also this method can be applied to CBR and VBR conditions because of using fluid flow model.Lastly, we discuss spatial, temporal information and three derivative measurements based on human visual system. Then we present an objective video quality assessment algorithm. Compared with subjective quality measurement, it has advantages of lower cost and being more timesaving, and is more flexible to be used in various test environments; it overpasses the traditional objective quality measurements in its high correlation with human perception system. Experiment results showed this proposed method could effectively evaluate the objective video quality, which could be a useful tool in the domain of video signal processing and compressing.