Audio level here refers to the RTP header extensions (RFC 6464 client-to-mixer, RFC 6465 mixer-to-client) that carry each packet's loudness as a small value in the header, computed by the sender. Their value is that a server or client can know who is speaking and how loudly without decoding the audio at all — cheap and privacy-friendly. An SFU reads it to forward only the active speakers in a large call instead of everyone, saving bandwidth, and clients use it to drive the 'who's talking' highlight and active-speaker layout. It is a small but pivotal piece of plumbing that lets big conferences scale and gives the UI its speaker indicators essentially for free.
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
The audio level header extension lets a server pick active speakers without decoding audio, which is what makes large group calls affordable. Volume 5 covers audio level in detail within group call audio: bitrate and topology decisions, mixing versus forwarding, jitter buffers and diagnosing call audio problems by symptom. Written by Nikolay Sapunov, CEO at Fora Soft.
Using audio level to scale active-speaker detection in group calls?
Tell us your call sizes and media server, and we will design active-speaker selection on audio level and estimate server load. 250+ video products shipped since 2005.
