One-page reference: what a live caption is (timed, speaker-labelled WebVTT-style cues); the SFU-side ASR fan-out pattern (tap audio at the SFU, VAD-gate recognition, fan caption text out over the data channel); the client-vs-server cost math ($13.86 naive vs $0.69 fan-out for a 1-hour 30-person call); partial-vs-final result handling; caption delivery over RFC 8831 data channels; the WCAG 1.2.4 Level AA / DOJ ADA April 2026 accessibility deadline; and a build-vs-buy checklist (mediasoup/Janus/Jitsi vs LiveKit; Deepgram/AssemblyAI/Whisper).
Download free PDF
The book · Volume 3 of 7
Video Streaming: A Complete Guide to Video Delivery: From ABR and CDNs to Players, WebRTC, DRM, and the Economics of Streaming
This live captions cheat sheet explains SFU-side ASR fan-out, the cost math that cuts a 30-person call from $13.86 to $0.69 an hour, and the WCAG deadline. Volume 3 covers the real-time side in detail: WebRTC and SFUs, data channels, subtitles in players, and the economics of delivery. Written by Nikolay Sapunov, CEO at Fora Soft.
Adding live captions to group calls without paying for speech recognition on every client?
Share your SFU and call sizes, and we will design the caption fan-out, pick the ASR vendor and estimate cost per call hour. 250+ video products shipped since 2005.
You get a realistic estimate, technical recommendations and next steps. Free, no obligations.
