An SFU (Selective Forwarding Unit) is the media-server architecture that makes large WebRTC conferences practical. Each participant sends their audio and video once to the SFU, which then forwards those streams to the other participants without decoding or mixing them. Keeping streams separate means the server's CPU cost is low (it just routes packets), every client can render participants individually, and the media stays encrypted between endpoints better than a mixing server allows. For audio, an SFU reads the per-packet audio-level marking to forward only the active speakers rather than everyone, saving bandwidth. SFUs are the dominant design for group calls today, sitting between the cheap-but-unscalable mesh and the heavy, latency-adding MCU.
The book · Volume 5 of 7
Audio for Video: A Complete Guide to Sound in Video Products: From Jitter Buffers and Lip Sync to Atmos, Quality Metrics, and Neural Codecs
An SFU is what lets a call grow past a handful of people, and its forwarding and bitrate decisions shape how audio holds up for every participant. This volume covers the SFU in depth next to MCU and mesh, with bitrate and topology decisions, jitter buffers and recording, so you can size and tune audio in group calls. Written by Nikolay Sapunov, CEO at Fora Soft.
Scaling SFU group calls and seeing audio quality drop as rooms grow?
Tell us your room sizes and traffic and we will review your SFU audio setup and give you a tuning and capacity plan. 250+ video products shipped since 2005.
