On Subpicture-based Viewport-dependent 360-degree Video Streaming using VVC

Virtual reality applications create an immersive experience using 360° video with high resolution and frame rate. However, since the user only views a portion of 360° video according to his/her current viewport, streaming the whole content with high resolution causes bandwidth wastage. To address this issue, viewport-dependent approaches have been proposed such that only the part of the video which falls within user's current viewport is transmitted in high quality while the rest of the content is transmitted in lower quality. The selection of high- and low-quality parts is constantly adapted according to the user's head motion, which requires frequent intra coded frames at switching points, leading to an increment in the overall streaming bitrate. In this paper a viewport-adaptive streaming scheme is introduced, which avoids intra frames at switching points by introducing long intra period for non-changing parts of the content during head motion. This scheme has been realized taking advantage of mixed Video Coding Layer (VCL) Network Abstraction Layer (NAL) unit feature of Versatile Video Coding (VVC) standard. This method reduces bitrate significantly, especially for the sequences with either no or only slow camera motion, which is common for 360° video capturing.