  This paper proposes a novel advanced motion model to handle the irregular
motion for the cubic map projection of 360-degree video. Since the irregular
motion is mainly caused by the projection from the sphere to the cube map, we
first try to project the pixels in both the current picture and reference
picture from unfolding cube back to the sphere. Then through utilizing the
characteristic that most of the motions in the sphere are uniform, we can
derive the relationship between the motion vectors of various pixels in the
unfold cube. The proposed advanced motion model is implemented in the High
Efficiency Video Coding reference software. Experimental results demonstrate
that quite obvious performance improvement can be achieved for the sequences
with obvious motions.
