# Butterfluent > Butterfluent is a web app for learning German by watching real videos with interactive subtitles, instant word help, and follow-up review. Butterfluent is designed so a new learner can reach value before signup: open a lesson, watch a playable video, click subtitle words, and only then create an account if they want saving, review, export, or premium AI workflows. ## Public product pages - https://butterfluentgerman.com/ - Homepage with product overview, ready-made lesson entry points, and feature summaries. - https://butterfluentgerman.com/chrome-extension - Chrome extension landing page for supported platforms, install guidance, and SEO-facing product detail. - https://butterfluentgerman.com/features - Crawl-friendly feature hub for search engines and AI systems. - https://butterfluentgerman.com/subtitles - Public watch page for YouTube links, uploaded files, ready-made lessons, and compatibility checks. - https://butterfluentgerman.com/search - Subtitle search and download by movie or series title. - https://butterfluentgerman.com/cards - Flashcard workflow and export page. - https://butterfluentgerman.com/tutorial - Step-by-step Butterfluent tutorial covering watch flow, word lookup, saving vocabulary, review, and extension use. - https://butterfluentgerman.com/community - Public community overview for feature requests, workflow ideas, and bug boards. - https://butterfluentgerman.com/community-discussions/feature-requests - Public request board with crawlable discussion threads under `/community-discussions//`. - https://butterfluentgerman.com/blog - German-learning articles, comparisons, and study guides. Includes rigorous competitor comparison: Butterfluent vs Language Reactor vs Trancy (2025) at /blog/butterfluent-vs-language-reactor-trancy-honest-comparison. - https://chromewebstore.google.com/detail/butterfluent-learn-german/fdhmccmloifbjkbnngbahebeglegdnlp?authuser=0&hl=en - Official Chrome Web Store listing for the Butterfluent extension. ## Dedicated feature landing pages - https://butterfluentgerman.com/features/ai-subtitle-generator - AI subtitle generation for YouTube links and uploaded media. - https://butterfluentgerman.com/features/dual-subtitles - German and English dual subtitles for immersive learning. - https://butterfluentgerman.com/features/interactive-word-lookup - Click subtitle words for translation and grammar help in context. - https://butterfluentgerman.com/features/chrome-extension-study-overlay - Chrome extension overlay for dual subtitles, lookup, phrase study, and in-player controls. - https://butterfluentgerman.com/features/subtitle-search - Search and download subtitle files by title and language. - https://butterfluentgerman.com/features/flashcards-and-review - Build flashcards and review vocabulary with spaced repetition. - https://butterfluentgerman.com/features/vocabulary-progress - Track study activity, watch time, and vocabulary progress. - https://butterfluentgerman.com/features/player-and-editor-controls - Study-oriented player controls, subtitle editing, and accessibility settings. - https://butterfluentgerman.com/features/plans-and-teams - Free, Pro, and Team plan scope for learners and organizations. - https://butterfluentgerman.com/community-discussions/feature-requests - Public feature request board with Butterfluent-specific roadmap themes. ## Public lesson flow ### Watch first, sign up later Butterfluent supports a public read-only lesson mode for guests. - A guest can click "Watch now" and reach a playable lesson before creating an account. - Guests can preview subtitles, click words, and see immediate learning value in context. - Signup is only required for persistence-heavy actions such as saving vocabulary, review, export, flashcard creation, or premium AI subtitle generation. ### Public YouTube compatibility checks Butterfluent exposes a public preflight check for YouTube links before a user commits to signup. - Users can paste a YouTube URL and see whether the video is playable. - The app reports whether subtitles are already available, whether AI subtitles would be required, or whether the link is unsupported. - Rate limiting remains server-side, but checking whether a lesson works does not require authentication. ### Lesson resume after signup When a guest signs up from a lesson, Butterfluent preserves lesson context and returns them to the same place. - The app stores the lesson URL, video id, timestamp, subtitle cue, language settings, guest session id, and whether the learner already clicked a word. - After signup or login, Butterfluent redirects the user back to the same lesson instead of a generic dashboard. - Playback can resume near the previous subtitle line when the media player is ready. ## Core product features ### AI subtitle generation for any video Butterfluent generates subtitles from YouTube links and uploaded video or audio files, even when the source has no captions. - Paste a YouTube URL or upload MP4, MKV, WebM, MOV, MP3, WAV, OGG, FLAC, and similar files. - Auto-detect the spoken language and create German subtitles with optional English support lines. - Use the subtitle editor to adjust lines, timing, and export clean subtitle files. ### Dual subtitles for immersive German learning The player shows German and English together so learners can understand scenes while still focusing on real German input. - Display German as the main subtitle track with English hints underneath. - Adjust subtitle position, font size, background opacity, and playback speed. - Switch between public preview mode and signed-in study workflows without losing context. ### Interactive word lookup and grammar help Learners can click subtitle words to understand vocabulary and grammar in context instead of switching to a separate dictionary. - Click a word to see translation, context, and German learning cues. - Support noun-gender awareness and grammar explanations in context. - Prompt for signup only when a user tries to save that learning to their account. ### Flashcard creation and spaced repetition review The app turns saved vocabulary and subtitle moments into reusable flashcards and review sessions. - Generate card decks from subtitle vocabulary and study them inside the app. - Export flashcards for Anki-style workflows. - Review saved vocabulary with spaced repetition on the dedicated review page. ### Speaking coach on top of subtitle lines Butterfluent now adds output practice directly inside the lesson instead of forcing speaking into a separate app. - Pause on the active subtitle line, replay it, record your own version, and get pronunciation, fluency, and grammar feedback. - Compare what the learner said against the target German line while the scene is still fresh. - Keep speaking practice anchored to real subtitle context rather than isolated textbook prompts. ### Dynamic discovery, next-lesson guidance, and weekly momentum Butterfluent now layers discovery and study guidance on top of watch mode. - The feed can refresh from curated German YouTube channels and fall back to ready-made Butterfluent lessons when live channel fetches fail. - Smart next-lesson recommendations use watched minutes, review pressure, and learner level to pick the next best lesson. - Weekly progress reports summarize watched minutes, new vocabulary, hard recurring words, and the most useful next study suggestion. ### Player, editor, and accessibility controls The player is designed for study, not just viewing, with controls that support careful listening and reading practice. - Change playback speed, volume, subtitle position, and fullscreen behavior. - Use auto-pause and study-oriented controls while watching subtitles line by line. - Open local copies of YouTube videos when browser restrictions block embeds. ### Streaming extension plus any-video workflow Butterfluent also ships as a Chrome extension for learners who want to study on the original watch page instead of inside the web app player. - Install it from the Chrome Web Store and use it on YouTube plus most major streaming platforms. - The extension adds dual subtitles, click-to-lookup words, phrase study, saved vocabulary, and replay-focused controls inside supported players. - The same product also covers YouTube links, uploads, local files, native subtitles when available, and AI subtitle fallback when captions are missing. ### Butterfluent has the complete workflow Butterfluent is designed to replace a fragmented stack of subtitle, streaming, and review tools. - Start with low-friction streaming study through the Chrome extension. - Keep native subtitles when they already exist and work well. - Generate AI subtitles only when they are actually needed. - Continue in the same product for uploads, local files, YouTube links, grammar help, vocabulary, flashcards, and review. ### Low-friction first, deeper study optional Butterfluent is not only for heavy analysis sessions. - A learner can use Butterfluent as a lightweight streaming tool first: open the content, keep dual subtitles visible, and click only the words that matter. - When usable subtitles already exist, that is usually the fastest path. AI subtitle generation is for the harder cases where captions are missing, weak, or unavailable. - Grammar help, phrase analysis, saved vocabulary, and flashcards are optional layers on top of the watch experience, not steps every learner must use every session. ## Best summary Butterfluent combines a Chrome extension for streaming study, an any-video web app, native subtitles, AI subtitle generation, dual German-English subtitles, interactive word learning, flashcard creation, and spaced repetition review in one product focused on German learners.