# Line 21 — Every voice, every language. Live Live captions, translations, and AI dubbing for streams, venues, and broadcast. Run it on our platform — or hand it to our team. Line 21 is a UK-based live captioning platform built on our own technology: an AI Proofreader that checks every caption against your event's names and jargon, and a cloud video encoder that puts captions into any stream. Around them we orchestrate 15+ AI models and professional human captioners, to deliver accurate captions, translations and AI dubbing in 100+ languages, live. ## Workflows ### Human captioning CART writers work the way they already work: your machine, your CAT software, our delivery. The platform is free for individual captioners and the agencies that book them. - Latency: 0.1s - Accuracy: 98% [More about Human captioning](https://line-21.com/services/human-live-captions) ### AI Captions & Translations RTMP, SRT, raw audio, or a bot in the meeting. 100+ languages. Multiple AI models behind one endpoint, because no single vendor wins on every language. - Latency: 3s - Accuracy: 95% - Languages: 100+ [More about AI Captions & Translations](https://line-21.com/features/speech-recognition) ### Video Encoding Custom cloud video encoder: CEA-608/708 into RTMP for broadcast and YouTube, multi-track SRT for several languages in one stream, HLS tuned for scale. Stream anywhere you already stream. - Latency: 5s [More about Video Encoding](https://line-21.com/features/caption-encoding) ### AI Dubbing Speech-to-speech, so the voice never round-trips through text. Real-time, low latency, priced for events that prefer not to fund an interpreter booth. - Latency: 10s [More about AI Dubbing](https://line-21.com/features/ai-dubbing) ## AI Proofreader An industry-first safeguard that learns the context of your event and corrects live captions before the audience sees them — names, jargon, and the line that was never meant to be funny. [How the AI Proofreader works](https://line-21.com/features/ai-proofreader) ## Destinations ### Browser link A URL or a QR on the seat. Captions, translations, and dubbed audio on any phone — no app, no login. [More about Browser link](https://line-21.com/features/integrations) ### Overlay Open captions over IMAG and in-room screens. Place the app on the picture, style the type, leave it there. [More about Overlay](https://line-21.com/features/integrations) ### YouTube & destinations CEA-608/708 in the stream you already send. YouTube, Twitch, Facebook, Vimeo, broadcast — captions live in the player's CC button. [More about YouTube & destinations](https://line-21.com/features/caption-encoding) ### HLS streaming We package the stream, insert every language, and host it on a global CDN. Viewers pick a language as closed captions — HLS is the format that actually allows that. - Multi-language closed captions - AI Dubbing - Global CDN - Our player or yours [More about HLS streaming](https://line-21.com/features/hls-streaming) ## What customers say Rated 4.0 out of 5 from 4 reviews on [Trustpilot](https://www.trustpilot.com/review/line-21.com). > **For several years we have been searching…** — Nils Bryntesson, SE, 5 October 2026 > For several years we have been searching for a solution where we could do closed captions, using the broadcast standard CEA 608-708 with human captioners, to Youtube Live. Line-21 has been the first service provider, out of quite a few, that was able to reliably make this work. > The staff has been incredibly service minded and agile when problems has arisen or when we’ve had requests out of the ordinary. We are also in joint development for new services that are required in our local market. Thus far we are very happy with our cooperation! > **Exceptional Partner for Our Business** — Darian Ghassemi, US, 2 December 2025 > We've had an outstanding experience working with Line 21. From day one, they've demonstrated professionalism and delivered a service that clearly puts the customer first. > What really sets them apart is their team. Paul and Fabrizio are incredibly communicative, transparent, and open throughout every stage of our collaboration. They're responsive, proactive, and make it easy to stay aligned on goals and deliverables. > Line 21 has proven to be more than just a client; they're a true partner. They've made collaboration simple and effective, which is exactly what you want when working with an external team. I'd highly recommend them to anyone looking for a reliable and professional partner. > **Nous avons travaillé avec Line21 dans…** — Nathalie MOREL, FR, 25 November 2025 > Nous avons travaillé avec Line21 dans le cadre du sous-titrage multilingue d'un événement interne. Toute l'équipe s'est montrée disponible et réactive et l'événement fût un grand succès grâce à la qualité du sous-titrage. Je ne peux que recommander Line21! > **Solid systm, solid support** — Jody Botting, GB, 14 November 2025 > The level of support and approachable attitudes of the team fills me with confidence every time. Not only am I using a product that excels, but there are friendly faces there to guide you if you need it - thank you Line 21! ## Community - **Discord**: This is our home. Here you can chat with us, get latest updates, real-time support, etc. - **Docs**: This is our knowledge center. Here you find out how to use Line 21, from general use cases down to specifics. - **Social Media**: This is where the fun is. We are present on several social media networks where we cover Line 21 and industry updates. Discord: https://discord.gg/ZgCYyXywCE · LinkedIn: https://www.linkedin.com/company/line-21-captions/ · YouTube: https://www.youtube.com/@ccbyline21