Vidaptive: Efficient and Responsive Rate Control for Real-Time Video on Variable Networks

TL;DR

Vidaptive introduces a novel rate control mechanism for low-latency real-time video streaming that decouples encoder decisions from network congestion, resulting in higher video quality and lower latency on variable networks.

Contribution

The paper presents Vidaptive, a new rate control system that improves responsiveness and video quality by decoupling encoder bitrate from network conditions using delay-based congestion control.

Findings

Achieves 1.5x higher video bitrate on cellular traces.

Improves SSIM, PSNR, and VMAF metrics significantly.

Reduces 95th-percentile frame latency by 2.2 seconds.

Abstract

Real-time video streaming relies on rate control mechanisms to adapt video bitrate to network capacity while maintaining high utilization and low delay. However, the current video rate controllers, such as Google Congestion Control (GCC), are very slow to respond to network changes, leading to link under-utilization and latency spikes. While recent delay-based congestion control algorithms promise high efficiency and rapid adaptation to variable conditions, low-latency video applications have been unable to adopt these schemes due to the intertwined relationship between video encoders and rate control in current systems. This paper introduces Vidaptive, a new rate control mechanism designed for low-latency video applications. Vidaptive decouples packet transmission decisions from encoder output, injecting ``dummy'' padding traffic as needed to treat video streams akin to backlogged flows controlled by a delay-based congestion controller. Vidaptive then adapts the target bitrate of the encoder based on delay measurements to align the video bitrate with the congestion controller's sending rate. Our evaluations atop Google's implementation of WebRTC show that, across a set of cellular traces, Vidaptive achieves ~1.5x higher video bitrate and 1.4 dB higher SSIM, 1.3 dB higher PSNR, and 40% higher VMAF, and it reduces 95th-percentile frame latency by 2.2 s with a slight 17 ms increase in median frame latency.