API
The Line 21 REST API: work with projects and captions programmatically from any language, with JSON requests and responses, plus a link to the full reference.
Overview
Jump to the full API documentation
Line 21 API enables developers to interact with the system programmatically.
The platform provides a REST API which can be interacted with through HTTP and from any programming language with all requests and responses encoded in JSON format.
The API currently supports two actions with other expanded functionality planned for future releases:
- Caption production: add external captions to a project
- Caption retrieval: download recorded captions for a project in various formats
Authentication
Authentication is based on the usage of a Bearer Token linked to a project.
In your project dashboard navigate to API in the left sidebar and copy the API Key.
Each request must contain an Authentication header with Bearer <api_key> as content.
Note: the API key is unique to the project not to the organisation. This is useful especially if you work with different partners or clients for different projects.
Endpoints
Send your requests to https://caption.line-21.com/api/v1 with JSON-encoded payloads.
For comprehensive endpoint documentation, request/response schemas, and interactive examples, visit the complete API documentation.
Example request
You can see an example using cURL from command line
curl -X POST "https://caption.line-21.com/api/v1/captions" \
-H 'accept: application/json'\
-H 'authorization: Bearer <your_api_key>'\
-H 'content-type: application/json' \
-d '{"projectId":"prj-id-123","language":"en","text":"The lazy fox...","timestampStart":1687344200000,"timestampEnd":1687344250000,"isInterim":false}'Future plans
We're actively expanding the API to provide complete programmatic control over the Line 21 platform. Upcoming features include:
- Organization and project management endpoints
- Organization-level API keys with granular permissions
- Multi-key support for enhanced security and access control
- Full coverage of all platform capabilities
Contact us if you have any questions or feedback about the API, including requests for new endpoints or features.
HLS streaming
Turn an RTMP or SRT feed into an HLS stream with multiple caption tracks, so viewers can pick their language in your own player or the Line 21 player.
Project management
Tools for project managers, AV technicians and accessibility specialists to supervise live captioning events in Line 21, alone or with invited team members.