DualSubs - Language Learning Subtitles

A Chrome extension for learning languages by watching Netflix, YouTube, Prime Video, and Disney+ with dual subtitles.

• Dual Subtitles: Display two language subtitles simultaneously
• Word Hover Definitions: Hover over any word to see instant dictionary definitions
• Offline Translation: Translate subtitles offline using Bergamot WASM
• Language Packs: Download only the languages you need
• Platform Support: Netflix, YouTube, Prime Video, Disney+

• TypeScript + React
• Vite + @crxjs/vite-plugin (Chrome extension bundling)
• AssemblyScript (Dictionary WASM)
• Bergamot Translator (Offline translation WASM)
• IndexedDB (Local storage)

• Node.js 18+
• npm or yarn

# Install dependencies
npm install

# Build the extension
npm run build

# Development mode with hot reload
npm run dev

# Build AssemblyScript dictionary module
npm run build:wasm

1. Open Chrome and navigate to chrome://extensions/
2. Enable "Developer mode" (toggle in top right)
3. Click "Load unpacked"
4. Select the dist folder

src/
├── manifest.json           # Extension manifest (Manifest V3)
├── background/
│   └── service-worker.ts   # Background service worker
├── content/
│   ├── index.ts            # Content script entry
│   ├── adapters/           # Platform-specific subtitle extraction
│   │   ├── youtube.ts
│   │   ├── netflix.ts
│   │   └── ...
│   ├── subtitle-controller.ts
│   └── overlay/            # React subtitle overlay UI
├── popup/                  # Settings popup UI
├── wasm/
│   ├── dictionary/         # Dictionary lookup integration
│   └── bergamot/           # Translation integration
├── storage/                # IndexedDB wrapper
└── shared/                 # Shared types and utilities

assembly/                   # AssemblyScript source
public/
├── icons/
└── wasm/                   # Compiled WASM files

Each streaming platform requires a specific adapter to extract subtitles:

• YouTube: Intercepts /youtubei/v1/player API for caption track URLs
• Netflix: Intercepts /metadata requests for TTML subtitle URLs
• Prime Video: Monitors network for WebVTT subtitle files
• Disney+: Intercepts subtitle playlist requests

Language packs contain:

• Dictionary data (~50-100MB per language)
• Bergamot translation model (~15-32MB per language pair)

Packs are downloaded on-demand and stored in IndexedDB.

Uses ExtensionPay for $5 one-time purchase:

• Free tier: Limited to 1 language pair
• Paid: All language pairs unlocked

# Full production build
npm run build

# The extension will be in the `dist` folder
# Zip for Chrome Web Store submission

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Submit a pull request

MIT