Research On Multi-Type Tree Partitioning And Rate Control Algorithm For Virtual Reality Video In VVC

In recent years,virtual reality technology(VR)has developed rapidly,and Virtual Reality 360-degree videos(later referred to as 360-degree videos)have become increasingly popular.Before encoding,360-degree video needs to be projected into a two-dimensional image,and the most common projection method at present is Equirectangular projection(ERP).Adopting this type of projection causes360 degree video to be stretched heavily in high-latitude areas,which affects encoding efficiency.Based on the characteristics of ERP video,the paper proposes an early decision algorithm with multi-type tree block division patterns and a rate control algorithm based on CTU(Coding Tree Unit)information entropy to improve the coding speed and coding performance respectively.First,to address the problem of high complexity caused by traversing all division patterns in the multi-type tree division process for 360-degree videos,the paper investigates the CU(Coding Unit)division process in ERP projection format.It is statistically found that the stretching phenomenon of ERP video affects the mode selection of VVC(Versatile Video Coding)coding unit division,resulting in a higher probability of selecting horizontal division modes.The paper proposes a fast division algorithm based on the empirical variogram and the Mahalanobis distance,designs a metric for measuring directional discrepancy and optimises the selection of thresholds according to CU sizes.Experimental results show that compared with VTM(VVC Test Model)4.0,the algorithm saves 32.13% of coding time with only 0.66% increase in BDBR(Bjontegaard Delta Bit Rate).Second,the paper studies the rate allocation algorithm of virtual reality video under ERP projection.To address the characteristics of the large amount of redundant data in the bipolar region of ERP projection,the paper proposes a rate control algorithm based on CTU information entropy.The algorithm designs a weighted CTU-level bit allocation scheme,which redistributes the rate by adjusting the weight of the CTU in the high-information area and the low-information area.Experimental results show that compared with VTM4.0,BDBR under Lowdelay configuration is reduced by 1.29% on average,and encoding time is only increased by 6.13% on average;BDBR under Randomaccess configuration is reduced by 0.66% on average,and encoding time is only increased by 1.8% on average.