RED (Redundant audio data, RFC 2198) is a simple, effective way to survive packet loss in real-time audio: each RTP packet carries not only the current frame but also a copy of one or more recent frames. If a packet is lost, its payload arrives anyway inside the next packet, so the receiver reconstructs the gap with no retransmission and no delay. It is codec-agnostic — wrapping whatever payload you use — and trades bandwidth for resilience, the redundancy roughly multiplying the audio bitrate. WebRTC uses RED, often combined with Opus's own in-band FEC, on lossy paths. The more redundancy you add the more loss you survive, but the more bandwidth you spend.
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
RED doubles up audio payloads so a single lost packet costs nothing, but on a congested link that extra bitrate can make loss worse. This volume covers RED in depth with in-band FEC, packet loss concealment, jitter buffers and bitrate decisions, so you can pick the right redundancy for each network profile. Written by Nikolay Sapunov, CEO at Fora Soft.
Considering RED redundancy for WebRTC audio on lossy mobile networks?
Tell us your loss patterns and bitrate budget and we will test RED against Opus in-band FEC and recommend settings per network profile. 250+ video products shipped since 2005.
