Video Coding Optimization for Virtual Reality 360Degree Source To provide excellent visual experience for customers, virtual reality (VR) sources require higher resolutions and better visual quality than traditional picture sequences. The content of a VR video can be mapped into a sphere by playing devices to present a   360circ    scene, which is usually called VR360xc2xa0in industrial community. The most popular formats for VR360 sources are the equirectangular projection (ERP) and the cubemap projection (CMP). Both ERP and CMP pictures can be effectively projected to a virtual threedimensional spherical surface for rendering. It brings a new challenge to the compression of VR video sources, which is how to reallocate proper bitrate to match mainstream projection formats. The most intuitive way to deal with this challenge is to empirically assign a fixed quantization parameter (QP) to each coding unit according to its position, which evidently lacks precision, rationality, and thus, degrades coding performance. This research proposes a new entropy equilibrium optimization (EEO) methodology to enhance the coding performance of VR360 videos. Specifically, we develop a spherical bitrate equalization strategy to obtain a blocklevel Lagrangian multiplier (  lambda  ,   lambda  ) for the ratedistortion optimization process in video coding. The appropriate QP value for each block is then dynamically determined in accordance with its   lambda  . Based on our EEO methodology, we develop two algorithms, EEOAERP and EEOACMP, to enhance compression efficiency for the ERP and CMP pictures, respectively. Experimental results demonstrate that both algorithms achieve significant BDRate savings and outperform the HM16.17 platform for allintra (AI), lowdelay (LD) and randomaccess (RA) configurations, respectively. Concretely, compared with the stateoftheart algorithm WSUERP, the proposed EEOAERP achieves BDRate saving of 0.37% in LD configuration. Furthermore, the proposed EEOACMP gains 2.6% on objective quality in RA configuration when compared with the HM16.17 VR CMP under the common test condition.

Adaptive QP with Tile Partition and Padding to Remove Boundary Artifacts for 360 Video Coding To adapt to existing highefficiency video coding standards or technologies, 360 video is represented by different projection formats with one or multiple planes. However, continuous spherical content will have discontinuous boundaries on representation planes, which results in obvious artifacts on viewing viewports rendered from coded projection formats. To solve this subjective issue, a boundary based adaptive QP method together with tile partition and padding is proposed in this paper. Tile partition and padding can effectively reduce obvious seam artifacts. Boundary areas are coded with better quality by using lower QP to further reduce visible artifacts. Experiments are conducted based on hybrid equiangular cubemap projection (HEC). Experimental results show that the proposed method can significantly improve subjective quality by removing boundary artifacts for 360 video coding.