By Aishu Menon Aishu Menon
on Speech-to-Text Transcription

Line 21

Hybrid human + AI captions for live events

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What Is Line 21?

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Line 21 is a UK-based live captioning solution built to make events and streams accessible to global audiences. It combines professional human captioners with AI tools such as automatic speech recognition, AI proofreading, and AI translations to deliver accurate, real-time captions.

The platform supports common live formats including web conferencing, live streaming, hybrid events, and browser-based viewing. Audio can be routed from platforms like Zoom, Microsoft Teams, YouTube, Twitch, RTMP, and HLS into Line 21, then captions can be distributed to multiple outputs.

With support for over 100 languages and pay‑as‑you‑go hourly pricing, it suits festivals, conferences, webinars, corporate meetings, and agency-managed productions.

Quick Snapshot

Line 21 blends professional human captioners with AI speech recognition and translation to deliver accurate, real-time captions for global audiences. Its flexible integrations and pay‑as‑you‑go pricing help organizers improve accessibility without adding workflow complexity.

Works on
  • Web
  • API
  • Other
Pricing Model
Subscription
Starting at €3/hour — Line 21 uses a pay‑as‑you‑go model, with rates starting at €3/hour for caption minutes. Additional hourly charges apply for human captioners, AI proofreading, AI translations, ASR, RTMP encoding, and HLS streaming.
Fits on
Affiliate Program
We could not identify an affiliate program.
API Availability
Line 21 has an API available.
Key Features
  1. Accurate live captions powered by humans and AI
  2. Seamless integrations with major streaming platforms
  3. Pay‑as‑you‑go pricing for flexible event needs
Audience
  • event organizers
  • conference producers
  • webinar hosts
  • streaming platforms
  • accessibility teams
  • corporate communication teams
  • education providers
  • digital agencies
URL
https://line-21.com

Screenshot

Line 21

Key Features of Line 21

Hybrid human + AI

Combines professional human captioners with automatic speech recognition, AI proofreading, and AI translations to deliver accurate, real-time captions.

Real-time captions

Generates and displays captions and translations live during events, streams, and online meetings for immediate audience accessibility.

100+ languages

Supports captioning and translation into more than 100 languages to serve international and multilingual audiences.

Streaming integrations

Connects with platforms like Zoom, Microsoft Teams, YouTube, Twitch, RTMP, and HLS, enabling flexible audio routing into Line 21.

Multiple output options

Distributes captions to various outputs, including browser-based viewers and streaming destinations, to match different event setups.

Pay‑as‑you‑go pricing

Charges per hour for caption minutes and related services, avoiding fixed plans and making it suitable for occasional or large-scale events.

API availability

Provides an API for integrating live captioning capabilities into custom workflows, platforms, or production pipelines.

Use Cases for Line 21

Virtual conferences

Provide accurate real-time captions and translations for conference sessions, making keynotes and panels accessible to global audiences in over 100 languages.

Webinars and workshops

Add live captions to educational webinars and training sessions so participants can follow along more easily, including those with hearing impairments or non-native language skills.

Live streaming platforms

Enhance streams on YouTube, Twitch, and RTMP/HLS channels with professional captions, improving discoverability and viewer engagement.

Hybrid and in-person events

Support hybrid events and on-site productions with live captions viewable in browsers or integrated into event platforms, expanding accessibility without complex infrastructure.

Corporate communications

Caption internal town halls, all-hands meetings, and global announcements so distributed teams can engage in real time regardless of language or hearing ability.

Frequently Asked Questions

What is Line 21 and how does it work?

Line 21 is a live captioning platform that combines human captioners with AI tools to provide real-time captions and translations. You route audio from your streaming or conferencing platform into Line 21, which then generates and distributes captions to your chosen outputs.

Which platforms does Line 21 integrate with?

Line 21 works with common streaming and conferencing platforms, including Zoom, Microsoft Teams, YouTube, Twitch, RTMP, HLS, and browser-based viewing solutions.

Does Line 21 support multiple languages?

Yes, Line 21 supports over 100 languages for captions and translations, making it suitable for global and multilingual events.

How is Line 21 priced?

Line 21 uses a pay‑as‑you‑go model, charging per hour for services such as caption minutes, human captioners, AI proofreading, AI translations, ASR, RTMP video encoding, and HLS video streaming, with rates starting at €3/hour for caption minutes.

Is there a free version of Line 21?

No, Line 21 does not offer a free version. All services are billed on a pay‑as‑you‑go hourly basis.

Who should use Line 21?

Line 21 is designed for event organizers, conference producers, webinar hosts, streaming platforms, accessibility teams, corporate communication teams, education providers, and digital agencies that need reliable live captioning.

Does Line 21 offer an API?

Yes, Line 21 provides an API that allows you to integrate live captioning and translation capabilities into your own platforms and workflows.

Line 21 · Our Verdict

Line 21 stands out by combining human captioners with AI, which is a practical way to balance accuracy, speed, and scale for live events. Its wide integration support and per-hour pricing make it attractive for organizers who need professional-grade accessibility without long-term contracts.

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