Geometry-Based Motion Vector Scaling for Omnidirectional Video Coding

Virtual reality (VR) applications make use of 360° omnidirectional video content for creating immersive experience to the user. In order to utilize current 2D video compression standards, such content must be projected onto a 2D image plane. However, the projection from spherical to 2D domain introduces deformations in the projected content due to the different sampling characteristics of the 2D plane. Such deformations are not favorable for the motion models of the current video coding standards. Consequently, omnidirectional video is not efficiently compressible with current codecs. In this work, a geometry-based motion vector scaling method is proposed in order to compress the motion information of omnidirectional content efficiently. The proposed method applies a scaling technique, based on the location in the 360° video, to the motion information of the neighboring blocks in order to provide a uniform motion behavior in a certain part of the content. The uniform motion behavior provides optimal candidates for efficiently predicting the motion vectors of the current block. The conducted experiments illustrated that the proposed method provides up to 2.2% bitrate reduction and on average around 1% bitrate reduction for the content with high motion characteristics in the VTM test model of Versatile Video Coding (H.266/VVC) standard.