Modern video players employ complex algorithms to adapt the bitrate of the video that is shown to the user. Bitrate adaptation requires a tradeoff between reducing the probability that the video freezes (rebuffers) and enhancing the quality of the video. A bitrate that is too high leads to frequent rebuffering, while a bitrate that is too low leads to poor video quality. Video providers segment videos into short segments and encode each segment at multiple bitrates. The video player adaptively chooses the bitrate of each segment to download, possibly choosing different bitrates for successive segments. We formulate bitrate adaptation as a utility-maximization problem and devise an online control algorithm called BOLA that uses Lyapunov optimization to minimize rebuffering and maximize video quality. We prove that BOLA achieves a time-average utility that is within an additive term $O(1/V)$ of the optimal value, for a control parameter V related to the video buffer size. Further, unlike prior work, BOLA does not require prediction of available network bandwidth. We empirically validate BOLA in a simulated network environment using a collection of network traces. We show that BOLA achieves near-optimal utility and in many cases significantly higher utility than current state-of-the-art algorithms. Our work has immediate impact on real-world video players and for the evolving DASH standard for video transmission. We also implemented an updated version of BOLA that is now part of the standard reference player dash.js and is used in production by several video providers such as Akamai, BBC, CBS, and Orange.

中文翻译：

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BOLA：在线视频的近最佳比特率适应

现代视频播放器采用复杂的算法来调整显示给用户的视频的比特率。比特率自适应需要在降低视频冻结（重新缓冲）的可能性与提高视频质量之间进行权衡。太高的比特率会导致频繁的重新缓冲，而太低的比特率会导致较差的视频质量。视频提供商将视频分成短段，并以多种比特率对每个段进行编码。视频播放器自适应地选择要下载的每个片段的比特率，并可能为连续片段选择不同的比特率。我们将比特率自适应公式化为效用最大化问题，并设计了一种称为BOLA的在线控制算法，该算法使用Lyapunov优化来最小化重新缓冲并最大化视频质量。 $ O（1 / V）$ 对于与视频缓冲器大小有关的控制参数V，是最佳值的最大值。此外，与先前的工作不同，BOLA不需要预测可用的网络带宽。我们使用一组网络跟踪在一个模拟的网络环境中凭经验验证BOLA。我们证明，BOLA实现了近乎最佳的效用，并且在许多情况下，其效用远高于当前的最新算法。我们的工作对现实世界的视频播放器以及不断发展的DASH视频传输标准具有直接影响。我们还实现了BOLA的更新版本，现在已成为标准参考播放器dash.js的一部分，并由Akamai，BBC，CBS和Orange等多家视频提供商在生产中使用。