I. Introduction
As interests in virtual reality (VR) application rise, 360-degree videos are gaining its popularity. These videos provide a spherical representation of the scene, which can be viewed freely using head mounted displays (HMDs). To be compressed by standard encoders, these videos are converted to two-dimensions (2D) image planar format by projections such as equirectangular (ERP), equal-area (EAP) and cubemap (CMP). Currently, most 360-degree panoramic videos are provided in ERP format. Similar to Geographic Coordinate System (GCS), a point on a sphere can be located by latitude and longitude. In ERP format video, a point can be mapped to a 2D plane by simply defining longitude as value of horizontal coordinate and latitude as the vertical. To provide more realistic visual experience, most 360-degree videos are high resolution and high frame rate. Thus, efficient video coding tool is vital for virtual reality application.