Research On Rate Control Algorithms For Screen Content Video

As the development of multimedia and computer,a new type of video named as screen content video has becoming more and more popular.This type of video is generated by the computer.For example,animations and remote education videos are typical screen content videos.In order to improve the coding efficiency of screen content videos,some specialists extend the High Efficiency Video Coding(HEVC)standard and propose a new video coding standard to encode screen content videos,and name it as HEVC Screen Content Coding extension(HEVC-SCC).However,the rate control algorithm in HEVC-SCC is inherited from HEVC and the inherited R-? rate control model is designed for natural content videos.The establishment of R-? model is based on the relationship between the coding bits and distortion(R-D).But in fact,the R-D relationship of screen content videos is changed.Moreover,this R-? model does not take the characteristic of screen content video into consideration when the bit allocation and parameter update operations are conducted.Therefore,the R-? model is not suitable for screen content videos.This paper takes several researches on the characteristics of screen content videos,and proposes two rate control algorithms for screen content videos.The major contents of the dissertation are summarized as follows:1.The optimization of R-? model and intra-frame bit allocation method based on video contents for the screen content video.Contents in the screen content video contain text,screen images with low texture complexity and nature images captured by cameras.Coding these different video contents results in different R-D relationships.In view of this characteristic,the rate control method should be conducted for different video contents separately.Firstly,the coding tree units(CTU)in screen content videos are claasified into three types: Text-CTU,Screen ImageCTU and Nature Image-CTU.Then,three R-? models reflecting different R-D relationships of different CTUs are established,and the model parameters are updated on the basis of their own models.Furthermore,a bit allocation scheme for the region containing only one kind of CTU is determined before allocating bits for each CTU.Experimental results show that the proposed rate control algorithm achieves 0.637 d B BDPSNR increase under the Random Access configuration and 0.749 d B BDPSNR increase under the Low Delay configuration on average,compared to the default R-? models in HEVC-SCC reference software.2.A GOP and frame level bit allocation algorithm based on the characteristics of screen content videos.Compared with the conventional nature video which is captured by cameras,the scene in screen content videos changes frequently.The bit allocation algorithm in this paper is proposed according to this characteristic.Firstly,the mean square error(MSE)of adjacent frames is used to classify all frames in screen content videos into two types: scene changed frames and scene unchanged frames.At the GOP level,the bit allocation scheme is based on the number of the scene changed frames in the current GOP.At the frame level,the bit allocation scheme for scene changed frames is according to the ratios of MSE of all frames in a GOP,and the bit allocation scheme for scene unchanged frames is according to the relationship between the inter and intra frame complexity and coding bits.Experimental results show that the proposed bit allocation algorithm achieves 1.874 d B BDPSNR increase,compared to the default R-? model with an equal bit allocation method at frame level in HEVC-SCC.In comparison with the default R-? model with an unequal bit allocation method at frame level in HEVC-SCC reference software,the proposed algorithm achieves 0.875 d B BDPSNR increase.These experimental results verify the efficiency of our proposed algorithm.