AST - AI Subtitle Translator

# AST - AI Subtitle Translator Naturally translate subtitles from videos on the following websites into your preferred language using LLM-based AI. - Udemy: https://www.udemy.com/ - NVIDIA Academy: https://www.nvidia.com/en-us/training/academy/ - YouTube: https://www.youtube.com/ - Vimeo: https://vimeo.com/ - TED: https://www.ted.com/ # Key Highlights - Translate subtitles quickly with Google Translate, or connect an LLM for natural translations that consider context. - Use prompts to specify a translation style. - Customize the subtitle display style directly. - Supports multiple LLM providers, including commercial AI APIs, OpenAI-compatible APIs, and local servers. Choose providers, models, and API keys in Settings; see the Chrome Web Store Options-screen screenshot for the full supported-provider list. # Notes - 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.