AST

• Providers other than Google Translate require an API key.
• Create a Google AI API key and connect the free-tier Gemini 3.1 Flash Lite model to start AI translation with fast responses. (Recommended)
• Check each LLM API provider's policy for free allowances, limits, and any applicable charges.

# Main Features

• Subtitle translation for Udemy, NVIDIA Academy, YouTube, TED, and Vimeo videos
• Context-aware AI translation that considers the flow of the source subtitles
• Fast translation with Google Translate included by default
• Fast translation is displayed first while LLM translation is being prepared
• Choose a source subtitle language provided by the video (default: English)
• Subtitle display, position adjustment, and width adjustment
• Customize subtitle font, color, shadow, outline, background color, and opacity
• Translation styles: Natural, Lecture, Technical, Custom 1 (Star Instructor), and Custom 2
• Chunked and parallel translation for long-video subtitles, plus a translation cache
• Password-encrypted backup and restore for settings, including API keys
• If AI translation fails, source subtitles remain visible and Google Translate is used as a fallback when available

# How To Use

• Google Translate is available by default after installation.
• Click the `AST` icon in the video toolbar, then turn on the `AI Subtitle Translation` toggle.

## Simple Settings — Recommended 1. Install the extension, then click the `Get API key` link at the bottom of Simple Settings to create a Google AI API key. 2. Enter the free API key in the `Google AI API key` field in Settings, then click `Check API key`. After verification succeeds, the Google AI provider and the `gemini-3.1-flash-lite` model are configured automatically.

See the introduction website's [LLM selection guide](https://mungi.github.io/ai-subtitle-translator/#llm-selection-guide) for first-time model recommendations.

## Advanced Settings

• To use a provider that requires an API key, enter the key issued by that provider, then click `Test connection`.
• Adjust the translation style and subtitle display style as needed.
• Back up all settings, including API keys. Backup files are encrypted with AES-256-GCM, and the password used during backup is required to restore them.
• If you have a DeepL API key, you can use DeepL for fast translation.

# Major Changes [ v0.1.3 (2026-08-03) ]

• Added support for ted.com.
• Improved API key visibility controls, fallback translation notices, and the stability of subtitle and provider-menu behavior.

[ v0.1.2 (2026-07-19) ]

• Added Simple Settings mode.

# Project Information

• License: MIT License
• Source: https://github.com/mungi/ai-subtitle-translator
• Site: https://mungi.github.io/ai-subtitle-translator/
• Issue reports and feature requests: https://github.com/mungi/ai-subtitle-translator/issues

# Privacy And Data Handling

• Privacy policy: https://mungi.github.io/ai-subtitle-translator/privacy-en.html
• Subtitle text may be sent to the translation provider selected by the user.
• API keys, settings, and the translation cache are stored only in the user's browser.
• API keys are stored as provider-specific ciphertext in browser storage and are not left as plaintext in settings data.
• Storage access is restricted to trusted extension contexts, and API keys are not exposed to content scripts.
• The extension does not store API keys on its own server or in an external database.
• API keys are sent directly to the selected provider when needed for authentication.
• Hosted providers are limited to their official HTTPS origins. Custom LLM can use HTTP or HTTPS on `localhost` or `127.0.0.1`, plus a user-selected custom HTTPS origin after the user approves access while fetching models or testing the connection; redirect responses are not followed automatically.