Manual Captioning
ASR
RTMP Streaming
HLS Streaming
Ai Translations
Ai Proofreader
Ai Context Builder
Embeddable Player
Meeting Bot
Caption Encoding
CEA 608/708
Playlists
Caption Playback
Caption View Page
Overlays
API
Manual Captioning
ASR
RTMP Streaming
HLS Streaming
Ai Translations
Ai Proofreader
Ai Context Builder
Embeddable Player
Meeting Bot
Caption Encoding
CEA 608/708
Playlists
Caption Playback
Caption View Page
Overlays
API
Manual Captioning
ASR
RTMP Streaming
HLS Streaming
Ai Translations
Ai Proofreader
Ai Context Builder
Embeddable Player
Meeting Bot
Caption Encoding
CEA 608/708
Playlists
Caption Playback
Caption View Page
Overlays
API
Manual Captioning
ASR
RTMP Streaming
HLS Streaming
Ai Translations
Ai Proofreader
Ai Context Builder
Embeddable Player
Meeting Bot
Caption Encoding
CEA 608/708
Playlists
Caption Playback
Caption View Page
Overlays
API
YouTube
Twitch
Vimeo
Custom RTMP
Microsoft Teams
Microsoft Skycap
Zoom
ChatGPT
Claude
AWS
YouTube
Twitch
Vimeo
Custom RTMP
Microsoft Teams
Microsoft Skycap
Zoom
ChatGPT
Claude
AWS
YouTube
Twitch
Vimeo
Custom RTMP
Microsoft Teams
Microsoft Skycap
Zoom
ChatGPT
Claude
AWS
YouTube
Twitch
Vimeo
Custom RTMP
Microsoft Teams
Microsoft Skycap
Zoom
ChatGPT
Claude
AWS
Intelligent
Live Captioning
100+ languages
15+ integrations
10+ AI models
Manual Captioning
ASR
RTMP Streaming
HLS Streaming
Ai Translations
Ai Proofreader
Ai Context Builder
Embeddable Player
Meeting Bot
Caption Encoding
CEA 608/708
Playlists
Caption Playback
Caption View Page
Overlays
API
Manual Captioning
ASR
RTMP Streaming
HLS Streaming
Ai Translations
Ai Proofreader
Ai Context Builder
Embeddable Player
Meeting Bot
Caption Encoding
CEA 608/708
Playlists
Caption Playback
Caption View Page
Overlays
API
Manual Captioning
ASR
RTMP Streaming
HLS Streaming
Ai Translations
Ai Proofreader
Ai Context Builder
Embeddable Player
Meeting Bot
Caption Encoding
CEA 608/708
Playlists
Caption Playback
Caption View Page
Overlays
API
Manual Captioning
ASR
RTMP Streaming
HLS Streaming
Ai Translations
Ai Proofreader
Ai Context Builder
Embeddable Player
Meeting Bot
Caption Encoding
CEA 608/708
Playlists
Caption Playback
Caption View Page
Overlays
API
YouTube
Twitch
Vimeo
Custom RTMP
Microsoft Teams
Microsoft Skycap
Zoom
ChatGPT
Claude
AWS
YouTube
Twitch
Vimeo
Custom RTMP
Microsoft Teams
Microsoft Skycap
Zoom
ChatGPT
Claude
AWS
YouTube
Twitch
Vimeo
Custom RTMP
Microsoft Teams
Microsoft Skycap
Zoom
ChatGPT
Claude
AWS
YouTube
Twitch
Vimeo
Custom RTMP
Microsoft Teams
Microsoft Skycap
Zoom
ChatGPT
Claude
AWS
Trusted by
State-of-the-art
We have developed a modern and highly flexible software to power your live captioning needs.
General Settings
General Settings
Language Settings with ASR
Language Settings with ASR
Translation Settings
Translation Settings
Ai Context BUilder
Ai Context BUilder
AI Proofreader Settings
AI Proofreader Settings
HLS Player Settings
HLS Player Settings
Live Flow Monitor
Live Flow Monitor
Download Assets
Download Assets
Caption View Settings
Caption View Settings
Simple Caption View
Simple Caption View
Human Captioner Interface
Human Captioner Interface
HLS Video Player with Mutiple Languages
HLS Video Player with Mutiple Languages
Live Captioning Services
Line 21 is a complete and highly flexible solution for your live captioning needs.
Human or Ai Captioning?
Line 21 supports both. Use expert humans for high-stakes events, AI for speed and scale — or mix them. Either way, you still get our powerful extras: AI Proofreader, live translations, synthetic voice, multi-destination output, and others.
AI Proofreader
Our AI Proofreader is an industry-first feature that learns the context of your event and delivers real-time corrections to live captions before your audience sees them. It’s your last line of defense against misnaming and errors.
From Youtube to browser link
Whether you're streaming on media platforms (YouTube, LinkedIn, Vimeo, Twitch, etc.), or you need captions in venues or browser links — Line 21 integrates seamlessly with a wide variety of destinations. RTMP and HLS streaming included. Plug in once, reach everyone.
Speak over 100 languages
Line 21 supports over 100 languages — whether through human captioning, translated in real-time, or captioned via ASR. From original speech to translated subtitles, we make sure your message travels clearly across cultures, borders, and platforms.
Built different
Line 21 combines breakthrough AI — like our real-time Ai Proofreader — with hands-on support and unmatched flexibility. From giant livestreams to quiet hybrid meetings, we adapt to your setup and your language. No one else in this space brings this much power and care together.
What is Line 21?
Line 21 is a UK-based live captioning agency making global events accessible. With our unique mix of human captioners and AI agents, we deliver real-time captions in 100+ languages — accurate, scalable, and ready for any stage or stream across the globe.
We reached out to Line-21 for a live broadcast for which we needed to translate closed captions from French to English. Contact was very easy and they understood our needs quite rapidly.
The team were very present for each technical test and made sure that everything was ready.
The event went well and our client was very satisfied with the quality and accuracy of the caption. We will definitely reach out to them for another project.
Nathalie Kueno
Customer success
Caast TV
Community
Discord
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Here you can chat with us, get latest updates, real-time support, etc.
Join our Discord serverDocs
This is our knowledge center.
Here you find out how to use Line 21, from general use cases down to specifics.
See DocumentationCreated by L21 Limited, 2023-2025.