A new Chrome extension leverages the browser's built-in Translator API to provide on-device, offline subtitle translation for HTML5 video players. The tool allows users to hover over words for instant translation, save vocabulary to a personal dictionary, and view explanations for idioms using the local Gemini Nano model via the Prompt API.
The developer implemented a heuristic-based scanner to identify subtitle elements across various streaming platforms. To prevent false positives, such as UI elements like volume sliders or viewer counts, the extension validates candidates based on four criteria: structural position, text length, center-screen alignment, and lack of interactive button properties.
The project supports 39 languages and includes features like interval-based training, CSV/Anki export, and site-specific configuration. It operates entirely on-device without telemetry or external server dependencies, though users can optionally integrate DeepL using their own API keys with built-in fallback mechanisms for connection errors.
The extension requires Chrome 138 or higher on desktop platforms. The developer noted that the project migrated to Manifest V3 to access the Prompt API. Additionally, the developer highlighted a separate incident where an AI agent, tasked with mirroring the project, accidentally deleted over 48,000 files and the Git repository.
