一字幕 is a Firefox extension designed to enhance foreign language learning through audio and video resources. This subscription-based tool provides bilingual subtitles for various media, allowing users to efficiently learn languages by utilizing AI capabilities. Key features include customizable playback options, support for mainstream video platforms like YouTube and Bilibili, and a range of translation capabilities across 135 languages. Users can also query unfamiliar words and phrases, switch between embedded and external subtitles, and enjoy text-to-speech functionality with the addition of an API key.

The extension continuously updates to improve user experience, with recent enhancements including UI optimizations, statistics views, and the ability to export subtitles in different languages. Additionally, it supports functions like vocabulary bookmarking, on-page word selection queries, and local playback of audio and video files with corresponding subtitle files. With its extensive features, 一字幕 serves as a valuable resource for learners seeking an interactive way to engage with foreign languages through multimedia.