CaptionFlow is a privacy-first, open-source video caption editor that runs entirely in your browser. It uses a high-performance stack (Rust, Wasm, WebGL) to handle transcription, editing, and video processing directly on your machine—no server uploads required.
- AI-Powered Transcription: Generate accurate subtitles using an in-browser version of Whisper. Your files stay local.
- High-Performance Timeline: A WebGL-rendered timeline provides a fluid UI for precise, frame-by-frame editing, even on longer videos.
- Client-Side Video Processing: Burn styled captions directly into your video file using FFmpeg compiled to WebAssembly.
- Standard Export Formats: Download your work as an
.srtfile for use on any platform. - Session Persistence: Your work is automatically saved to the browser's IndexedDB, so you can pick up where you left off.
Try the live version at captionflow.net.
Note: The AI models are fetched on first use, so the initial transcription may take a moment to start.
The core idea is to do as much as possible on the client-side, giving the user full control over their data and enabling a fast, desktop-like experience on the web.
- Rust → WebAssembly: Core editor logic, caption manipulation, and undo/redo history are handled in Rust for performance and safety.
- WebGL: The timeline and audio waveform are rendered via WebGL for a smooth UI that doesn't freeze, even with a lot of data.
- FFmpeg.wasm: For burning subtitles directly into the video file in the browser.
- whisper.cpp (Wasm): For high-quality, in-browser audio transcription.
- Frontend: Built with React, TypeScript, and Vite. Styled with Tailwind CSS.