Had You Looked Where I'm Looking: Cross-user Similarities in Viewing Behavior for 360∘^{\circ} Video and Caching Implications

The demand and usage of 360$^{\circ}$ video services are expected to increase. However, despite these services being highly bandwidth intensive, not much is known about the potential value that basic bandwidth saving techniques such as server or edge-network on-demand caching (e.g., in a CDN) could have when used for delivery of such services. This problem is both important and complicated as client-side solutions have been developed that split the full 360$^{\circ}$ view into multiple tiles, and adapt the quality of the downloaded tiles based on the user's expected viewing direction and bandwidth conditions. To better understand the potential bandwidth savings that caching-based techniques may offer for this context, this paper presents the first characterization of the similarities in the viewing directions of users watching the same 360$^{\circ}$ video, the overlap in viewports of these users (the area of the full 360$^{\circ}$ view they actually see), and the potential cache hit rates for different video categories, network conditions, and accuracy levels in the prediction of future viewing direction when prefetching. The results provide substantial insight into the conditions under which overlap can be considerable and caching effective, and can inform the design of new caching system policies tailored for 360$^{\circ}$ video.Comment: 13+ page