The delivery and display of 360-degree videos on Head-Mounted Displays (HMDs) presents many technical challenges. 360-degree videos are ultra high resolution spherical videos, which contain an omnidirectional view of the scene. However only a portion of this scene is displayed on the HMD. Moreover, HMD need to respond in 10 ms to head movements, which prevents the server to send only the displayed video part based on client feedback. To reduce the bandwidth waste, while still providing an immersive experience, a viewport-adaptive 360-degree video streaming system is proposed. The server prepares multiple video representations, which differ not only by their bit-rate, but also by the qualities of different scene regions. The client chooses a representation for the next segment such that its bit-rate fits the available throughput and a full quality region matches its viewing. We investigate the impact of various spherical-to-plane projections and quality arrangements on the video quality displayed to the user, showing that the cube map layout offers the best quality for the given bit-rate budget. An evaluation with a dataset of users navigating 360-degree videos demonstrates that segments need to be short enough to enable frequent view switches.
@cite_16: 
@cite_2: Interactive spatial navigation within a video is getting attention in the research community, especially in scenarios such as 360° video, video surveillance or region-of-interest viewing. With more content being delivered over the top, the complexity of spatial access to the video is increased by the need to perform bitrate adaptation to react to network variations. In this paper, we describe how spatial access can be performed in an adaptive HTTP streaming context, using tiling of the source content, MPEG-DASH and its SRD extensions. We describe a configurable implementation of these technologies, within the GPAC open-source player, allowing experimentations of different adaptation policies for tiled video content.
@cite_11: Delivering high resolution, high bitrate panorama video to a large number of users introduces huge scaling challenges. To reduce the resource requirement, researchers have earlier proposed tiling in order to deliver different qualities in different spatial parts of the video. In our work, providing an interactive moving virtual camera to each user, tiling may be used to reduce the quality depending on the position of the virtual view. This raises new challenges compared to existing tiling approaches as the need for high quality tiles dynamically change. In this paper, we describe a tiling approach of panorama video for interactive virtual cameras where we provide initial results showing the introduced overheads and the potential reduction in bandwidth requirement.
@cite_17: The mismatch between increasingly large video resolution and constrained screen size of mobile devices has led to the proposal of zoomable video systems based on tiled video. In the current system, a tiled video frame is constructed from multiple tiles in a single resolution stream. In this paper, we explore the perceptual effect of mixed-resolution tiles in tiled video, in which tiles within a video frame could come from streams with different resolutions, with the aim to tradeoff bandwidth and perceptual video quality. To understand how users perceive the video quality of mixed-resolution tiled video, we conducted a psychophysical study with 50 participants on tiled videos where the tile resolutions are randomly chosen from two resolution levels with equal probability. The experiment results show that in many cases, we can mix tiles from HD (1920×1080p) stream and tiles from 1600×900p stream without being noticed by the viewers. Even when participants notice quality degradation in videos combined with tiles from HD stream and tiles from 960×540p stream, the majority of participants still accept the degradation when viewing videos with low and medium motion; and greater than 40 of participants accept the quality degradation when viewing video with dense motion.
To deal with the cases of end-users consuming only a fraction of the video (navigable panorama @cite_16 @cite_17 @cite_11 and large-resolution video @cite_2 ), the most studied delivery solution leverages the concept of . The idea is to spatially cut a video into independent tiles. The server offers multiple video representations of each tile; the client periodically selects a representation for each tile and it has to reconstruct the full video from these tiles before the viewport extraction. In a short paper, have sketched a tile-based streaming system for @math -degree videos. In their proposal, the spherical video is mapped onto an video, which is cut into @math . More recently, proposed a -based tiling of a @math -degree video to take into account projection distortion. They also present an approach to describe the tiles with MPEG DASH SRD formatting principles. also propose the delivery of tiles based on a prediction of the head movements. evaluate the impact of different tiling scheme on the compression efficiency and on the transmission bit-rate saving.