An efficient coding algorithm for 360-degree video based on improved adaptive QP Compensation and early CU partition termination

Abstract

Virtual reality technology enables people to experience the video content immersively. In order to provide realistic presence and dynamic view, the virtual reality video requires higher resolution (4 K or 8 K) image and more data to display relative to traditional video. Therefore, to improve the coding efficiency of 360-degree video becomes a key consideration. In the coding of 360-degree video, the spherical image is projected to a 2D image (such as ERP projection) and the standard video coding framework is utilized to accomplish the rest work. However, such a projection introduces much different levels of distortion according to coordinates, which degrades performance of rate distortion optimization in video encoding process. In this paper, we propose a compression optimization algorithm by using adaptive QP compensation based on coordinates to improve compression efficiency, and utilizing early termination of CU partition based on spatial correlation to reduce encoding time. To further reduce encoding complexity, the prewitt operator and the adaptive mode selection are adopted to reduce unnecessary intra prediction modes. Experimental results show that compared with HM-16.16, the proposed algorithm can reduce time by 42.4%, increase WSPSNR by 0.03 and decrease BD-rate by 0.3%.