BOLA: Near-Optimal Bitrate Adaptation for Online Videos

TL;DR

BOLA is an online bitrate adaptation algorithm for streaming videos that optimizes video quality while minimizing rebuffering, without needing network bandwidth prediction, and is proven to be near-optimal and widely adopted.

Contribution

We introduce BOLA, a novel Lyapunov optimization-based algorithm for bitrate adaptation that achieves near-optimal utility without bandwidth prediction, and demonstrate its effectiveness through theoretical analysis and real-world deployment.

Findings

BOLA achieves utility within O(1/V) of the optimal.

BOLA outperforms existing algorithms in simulations.

BOLA is adopted in production by major video providers.

Abstract

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.