Recent advances in omnidirectional video coding for virtual reality: Projection and evaluation

In this paper, we review the recent advances in the pipeline of omnidirectional video processing including projection and evaluation. Being distinct from the traditional video, the omnidirectional video, also called panoramic video or 360 degree video, is in the spherical domain, thus specialized tools are necessary. For this type of video, each picture should be projected to a 2-D plane for encoding and decoding, adapting to the input of existing video coding systems. Thus the coding influence of the projection and the accuracy of the evaluation method are very important in this pipeline. Recent advances, such as different projection methods benefiting video coding, specialized video quality evaluation metrics and optimized methods for transmission, are all presented and classified in this paper. In addition, the coding performances under different projection methods are specified. The future trends of omnidirectional video processing are also discussed.