Recent advances in omnidirectional cameras and AR/VR headsets have spurred the adoption of 360-degree videos that are widely believed to be the future of online video streaming. 360-degree videos allow users to wear a head-mounted display (HMD) and experience the video as if they are physically present in the scene. Streaming high-quality 360-degree videos at scale is an unsolved problem that is more challenging than traditional (2D) video delivery. The data rate required to stream 360-degree videos is an order of magnitude more than traditional videos. Further, the penalty for rebuffering events where the video freezes or displays a blank screen is more severe as it may cause cybersickness. We propose an online adaptive bitrate (ABR) algorithm for 360-degree videos called BOLA360 that runs inside the client's video player and orchestrates the download of video segments from the server so as to maximize the quality-of-experience (QoE) of the user. BOLA360 conserves bandwidth by downloading only those video segments that are likely to fall within the field-of-view (FOV) of the user. In addition, BOLA360 continually adapts the bitrate of the downloaded video segments so as to enable a smooth playback without rebuffering. We prove that BOLA360 is near-optimal with respect to an optimal offline algorithm that maximizes QoE. Further, we evaluate BOLA360 on a wide range of network and user head movement profiles and show that it provides $13.6\%$ to $372.5\%$ more QoE than state-of-the-art algorithms. While ABR algorithms for traditional (2D) videos have been well-studied over the last decade, our work is the first ABR algorithm for 360-degree videos with both theoretical and empirical guarantees on its performance.

翻译：近年来，全景相机和AR/VR头戴显示设备的进步推动了360度视频的普及，这类视频被广泛认为是未来在线视频流媒体的发展方向。360度视频允许用户佩戴头戴显示设备（HMD），体验仿佛身临其境的视频场景。大规模高质量传输360度视频仍是一个未解决的问题，其挑战性远高于传统（2D）视频传输。360度视频所需的数据率比传统视频高出一个数量级。此外，视频卡顿或显示黑屏的缓冲事件造成的负面影响更为严重，可能引发晕动症。我们提出一种针对360度视频的在线自适应码率（ABR）算法——BOLA360，该算法运行于客户端视频播放器内，通过协调从服务器下载视频片段，最大化用户的质量体验（QoE）。BOLA360通过仅下载可能落入用户视野（FOV）的视频片段来节省带宽。同时，BOLA360持续适应下载视频片段的码率，以实现无缓冲卡顿的流畅播放。我们证明，BOLA360相对于最大化QoE的离线最优算法具有近最优性能。此外，我们基于广泛的网络和用户头部运动轨迹对BOLA360进行评估，结果表明其相比现有最优算法可提升13.6%至372.5%的QoE。尽管传统（2D）视频的ABR算法在过去十年中已得到充分研究，但我们的工作是首个在理论和实证层面均保证性能的360度视频自适应码率算法。