Bit-Rate Control Technique Of Video Coding With H.264/AVC Standard

To obtain the optimal reconstructed video quality, bit-rate control technology should be used to select the proper encoding parameters for encoders with the constrained resources. Since coding efficiency highly depends on the accuracy of the selected coding parameters, how to design an appropriate rate control method is a key enabling factor for video coding. This thesis investigates rate control mechanism in low bit-rate and real-time applications based on H.264/AVC video coding standard. Major contributions are summarized as follows:1. A method for ascertaining initial quantization parameter is designed in this thesis. In the designed method, the influence of image complexity on quantization parameter determination is taken into account, and an image complexity metric based on Sobel operator is presented. Furthermore, the relationship between the model parameter and the image complexity is studied. Due to the consideration of image complexity in the designed method, the obtained initial quantization parameter can adapt to the video complexity differences, thus improving the efficiency for encoders.2. Based on the analysis of traditional bit-rate control, a linear bit-rate control scheme is established and further demonstrated. With the established scheme, the quantization parameter can be determined directly, thus avoiding the round-off error, which is brought by the transformation from quantization step into quantization parameter. The experimental results show the established scheme can obtain favorable performance.3. Modification for frame skipping algorithm in low bit-rate. In this thesis, the statistical property for the relationship between coding efficiency and macro-block prediction modes is analyzed in low bit-rate, and then a method for reducing the probability of frame skipping is designed. In the designed method, the quantization parameter is updated in real time according to the buffer state, and the final coding modes are determined using the statistical property for the relationship between coding efficiency and macro-block prediction modes. The experimental result shows the designed method can reduce the probability of the occurrence of frame skipping in low bit-rate.