Modeling the Perceptual Quality for Viewport-Adaptive Omnidirectional Video Streaming Considering Dynamic Quality Boundary Artifact

Instead of streaming the entire omnidirectional video that induces a waste of bandwidth, the tile-based viewport adaptive streaming is preferred in practice. Tiles within users' viewport are transmitted in high quality, while tiles elsewhere are delivered in lower quality to reduce the network bandwidth consumption. In this setup, when users change their viewport, they may potentially be disturbed by the exposure of low-quality tiles and the subsequent quality refinement in a period of delay. We defined this phenomenon in the viewport as a Dynamic Quality Boundary (DQB) artifact, as there exists a clear boundary between low-quality tiles and high-quality tiles which appears, moves, and disappears along with the change of users' viewport. The DQB artifact is a specific quality degradation in the viewport-adaptive omnidirectional video streaming whose impact on users' perceptual quality has not been adequately studied. In this paper, we focused on investigating and modeling its impact on the quality perception of users when streaming omnidirectional videos. More specifically, systematic subjective quality evaluation experiments towards DQB artifact were designed and conducted. Accordingly, a perceptual quality metric was proposed considering the quality of tiles, the proportion of low-quality tiles, and the refinement duration. Experimental results, measured in various aspects, showed that the proposed metric can accurately predict users' perceptual quality of the tile-based viewport-adaptive omnidirectional video streaming service.