Buffer-based smooth rate adaptation for dynamic HTTP streaming

Recently, Dynamic Streaming over HTTP (DASH) has been widely deployed in the Internet. However, it is still a challenge to play back video smoothly with high quality in the time-varying Internet. In this paper, we propose a buffer based rate adaptation scheme, which is able to smooth bandwidth variations and provide a continuous video playback. Through analysis, we show that simply preventing buffer underflow/overflow in the greedy rate adaptation method may incur serious rate oscillations, which is poor quality-of-experience for users. To improve it, we present a novel control-theoretic approach to control buffering size and rate adaptation. We modify the buffered video time model by adding two thresholds: an overflow threshold and an underflow threshold, to filter the effect of short-term network bandwidth variations while keeping playback smooth. However, the modified rate adaptation system is nonlinear. By choosing operating point properly, we linearize the rate control system. By a Proportional-Derivative (PD) controller, we are able to adapt video rate with high responsiveness and stability. We carefully design the parameters for the PD controller. Moreover, we show that reserving a small positive/negative bandwidth margin can greatly decrease the opportunities of buffer underflow/overflow incurred by the bandwidth prediction error. At last, we demonstrate that our proposed control-theoretic approach are highly efficient through real network trace.