Experimental Evaluation of Simulcast for WebRTC

One of the important use cases for WebRTC is multi-party audio/video conferencing, and there are multiple services that offer that functionality. Two aspects that the maintainers of such services often try to optimize are the maximum size of their conferences, and the cost of their infrastructure. Simulcast is one approach to addressing these problems in conference systems that build upon video routers. It consists of the simultaneous transmission of multiple versions of a participant's video stream, which use different resolutions, frame rates and, most importantly, different bit rates. In this article we present the analysis and experimental evaluation of a conference system based on WebRTC using simulcast with the VP8 codec. We examine the computational and bandwidth requirements of both the server and the clients, as well as the end-to-end video quality. Our results show significant gains for the receivers and the infrastructure, with minor penalties to the image quality and resource usage for the senders.