Explore this section

• Core Idea -- The philosophy behind Deja and the three-step learning loop
• Key Features -- Subtitles, word lookup, phrase extraction, grammar analysis, spaced repetition, and more
• Name & Logo -- Why it's called DejaVocab and the hidden story in the logo

Traditional language learning starts from word lists and grammar rules. Deja takes the opposite approach: start from context.

When you watch a YouTube video, listen to a podcast, or read a book in Deja, every word, phrase, and sentence you encounter becomes part of your personal language corpus. The same expression appearing in different contexts reinforces your understanding naturally.

Deja is more like a Language Learning OS than a single-purpose app. It integrates fragmented content into a complete learning ecosystem, forming an effective loop with every watch, save, and review.

The Learning Loop

Deja implements a complete learning cycle in three steps:

1. Natural input -- Choose content you're genuinely interested in: YouTube videos, Bilibili, podcasts, TikTok, EPUB books, or local videos
2. Precise extraction -- The system generates subtitles, translations, and phrase breakdowns, highlighting key expressions. Save words, phrases, or sentences to your personal corpus with one tap.
3. Personalized review -- Saved items become flashcards with real context. The FSRS spaced repetition algorithm schedules reviews based on your memory patterns.

• Subtitle extraction & transcription -- Automatically fetch subtitles from YouTube and Bilibili, or generate high-quality AI subtitles via Deja Transcription or Local Transcription
• Context-aware word lookup -- Tap any word to see its meaning in the current context, not just generic dictionary definitions
• Word Family -- A single word entry automatically includes all common forms (noun, verb, adjective, adverb), making vocabulary learning systematic
• Phrase extraction -- AI automatically identifies idioms, phrasal verbs, collocations, and fixed expressions
• Grammar analysis -- Break down complex sentences into grammatical components with color-coded visualization
• AI translation -- Context-aware translation that considers surrounding sentences for better accuracy
• Spaced repetition -- All collected items become flashcards reviewed using the FSRS algorithm, with original audio and context
• Multi-language support -- Learn English, Chinese, Korean, Japanese, Russian, French, German, Italian, Spanish, and Portuguese (10 languages)
• PDF export -- Export your complete learning records for archiving, printing, or long-term review

Why "DejaVocab"?

The name comes from the French phrase déjà vu, meaning "already seen". In language learning, the most powerful moment is when you encounter a word or phrase you've seen before and think: "I've seen this somewhere!" -- that flash of recognition is déjà vu.

Deja + Vocab = the vocabulary you've already encountered. Deja turns that fleeting sense of familiarity into lasting memory by anchoring every word to the real context where you first met it.

The Logo: A Story Hidden in Plain Sight

The Deja logo is a circular serpent -- an Ouroboros -- shaped as a Möbius strip. These two symbols represent the core philosophy of the app:

• Ouroboros -- The ancient symbol of a snake eating its own tail represents the endless cycle of learning: encounter → save → review → encounter again, deeper each time.
• Möbius strip -- A surface with only one side, symbolizing how input and review are not separate stages but one continuous, seamless loop.

Look closely at the serpent and you'll notice a bump in its middle. Most people see a hat. But it's actually an elephant swallowed by a boa constrictor -- a direct reference to The Little Prince by Antoine de Saint-Exupéry.

In the book, the narrator draws a boa that has swallowed an elephant whole. Adults always say it looks like a hat. Only children -- and the Little Prince -- see the truth. This is the spirit of Deja: look deeper, see more. Language is not just words on a screen; it carries stories, emotions, and the voice of the speaker. Deja helps you see what's really there.

How to import

• In the app -- Tap the search icon on the home page, search for any YouTube video, and open it directly
• Paste a link -- Tap the + icon in the Corpus tab, paste a YouTube URL to import
• Chrome Extension -- Open any YouTube video in Chrome, click the Deja button that appears on the video player
• YouTube Shorts -- Short-form vertical videos are also supported. Import them using the same link-paste method.

Channel subscriptions

Tap the + icon on the home page to open the subscription management screen.

• Recommended Channels -- Deja provides admin-curated language learning channels, filtered by your target learning language. Categories include education, entertainment, news, science, and more.
• My Channels -- Sync your personal YouTube subscriptions by logging in with Google. Your actual YouTube subscriptions appear here for easy access.
• Subscribe / Unsubscribe -- Tap the button on any channel card to toggle your subscription. Subscribed channels appear as a horizontal scrollable row at the top of your home feed.
• Channel detail -- Tap any channel card to view its detail page with the latest videos. Open a video to start learning immediately.

YouTube Search

Tap the magnifying glass icon on the home page to search for any YouTube video directly within Deja.

• Search history -- Up to 10 recent queries are saved locally. Tap a history item to re-search, or swipe to delete.
• Channel results -- Matching channels appear as horizontal scrollable circles at the top of the results. Tap to view the channel detail page.
• Video results -- Each result shows thumbnail, title, channel name, duration, and view count. Tap to open in Deja's player with full learning features.
• Advanced filters -- Tap the filter icon for YouTube-style search filters: Content Type (video, channel, playlist), Duration (short / medium / long), Upload Date (today, this week, this month, this year), Sort By (relevance, upload date, view count, rating), and Features (subtitles, HD, 4K, etc.).
• Infinite scroll -- Scroll down to automatically load more results.

In this section

• Player & Controls -- Video playback, progress bar, speed control, subtitle display
• Subtitles & Learning -- Subtitle sources, word lookup, phrase extraction, sentence saving
• Troubleshooting -- Video won't play, login verification, VPN/proxy issues

Layout

The video player sits at the top of the screen, with the subtitle list below. As the video plays, the current subtitle is automatically highlighted and the list scrolls to keep it in view.

Bottom control bar

• Progress bar -- Drag to seek. Shows current time and total duration.
• Previous / Next sentence -- Jump to the previous or next subtitle. Great for sentence-by-sentence study.
• Sentence loop -- Toggle single-sentence repeat for intensive listening practice.
• Listening mode -- Switch to a focused listening view that shows only the current sentence with hide/reveal controls.
• Playback speed -- Choose from 0.5x, 0.75x, 1x, 1.25x, 1.5x, or 2x. Slower speeds help with difficult content.
• Language selector -- When multiple subtitle languages are available, switch between them.
• PDF export -- Export the complete subtitle transcript with translations and phrases as a PDF for printing or offline review.

Playback history

Deja automatically saves your playback position. When you reopen a video, it resumes from where you left off. This works across sessions -- close the app and come back days later, and your position is preserved.

Subtitle sources

• Platform subtitles -- Deja automatically fetches existing YouTube subtitles (auto-generated or manual). This is instant and free.
• Deja Transcription -- Re-transcribe with server-side AI for higher accuracy, natural sentence breaks, and proper punctuation. Consumes quota.
• Local Transcription -- Use on-device Whisper models. Free, but the app must stay open during processing.

Learning interactions

Once subtitles are loaded, every sentence becomes interactive:

• Tap a word -- Look up its context-aware definition. Saved words are highlighted across all your content.
• Swipe left -- Save the sentence to your corpus with one tap.
• Swipe right -- Open grammar analysis for the sentence.
• Phrase highlights -- Extracted phrases are highlighted in the subtitle text. Tap to see details.
• Translation -- AI translation appears below each subtitle. Supports rolling translation (translates as you watch).

Subtitle settings

• Font size -- Adjust subtitle text size in Settings.
• Show/hide translations -- Toggle translation display globally.
• Phrase highlighting -- Toggle phrase highlights, filter by type or CEFR level.
• Word highlighting -- Saved words are underlined in subtitles for visual tracking.

Video won't play / shows an error

This is the most common issue, especially for users outside the US/Europe. The root cause is related to how YouTube verifies embedded video requests.

Why does this happen?

Deja uses the YouTube iFrame Player API to embed videos. YouTube's servers check the HTTP request origin and referrer headers to verify that the embed is legitimate. When you use a VPN or proxy, YouTube may flag the request because:

• The IP address has been flagged for suspicious activity (shared VPN IPs are often abused)
• YouTube requires login verification to confirm you're not a bot
• The WKWebView (iOS) or WebView (Android) doesn't send proper referrer headers that match a regular browser

iOS: Fix video playback issues

On iOS, Deja uses WKWebView to embed YouTube. The iFrame API does not support showing a login prompt inside WKWebView, so if YouTube requires verification, the video simply won't play.

Solution: Switch to a clean VPN/proxy node. The issue is almost always caused by the VPN IP being flagged. Try:

• Switch to a different server/node in your VPN app
• Choose a less popular region (e.g., Japan, Singapore instead of US)
• Use a premium VPN service with dedicated (non-shared) IPs
• If possible, try connecting without a VPN to confirm the issue is VPN-related

Android: Login to bypass verification

On Android, Deja provides a YouTube login button in the top-right corner of the video player. Tap it to sign in with your Google account directly inside the WebView.

Once logged in, YouTube recognizes you as a legitimate user and stops requiring additional verification. This resolves most playback issues on Android even with VPN.

Why can I watch YouTube in the YouTube app but not in Deja?

This is one of the most frequently asked questions. The YouTube app and Deja access YouTube in fundamentally different ways:

• YouTube app -- You are logged into your Google account. YouTube recognizes you as a verified user and serves videos directly through its own proprietary protocol. No web embed restrictions apply.
• Deja -- Uses the YouTube iFrame Player API (an embedded web player). YouTube treats this as a third-party embed and applies stricter verification: checking your IP, referrer headers, and whether the request looks like a bot.

In short: the YouTube app has direct, authenticated access to YouTube's servers. Deja's embedded player goes through YouTube's web verification layer, which is much more sensitive to VPN/proxy IPs. That's why switching to a clean VPN node usually fixes the issue.

Other common issues

• Age-restricted videos -- Some videos require YouTube login to confirm age. On Android, use the login button. On iOS, these videos may not be playable.
• Region-restricted videos -- If a video is not available in your region, a VPN to the correct region is required.
• Private or unlisted videos -- Deja cannot access private videos. Unlisted videos work if you have the direct link.
• Slow loading -- Check your internet connection. YouTube videos stream directly from YouTube's servers, so Deja's servers are not involved in video playback.

How to access

On the home page (Subscribe tab), tap the + icon in the top-right corner to open "Manage Subscriptions".

Two tabs

• Recommended Channels -- Admin-curated language learning channels, filtered by your target learning language. Categories include education, entertainment, news, science, and more.
• My Channels -- Sync your personal YouTube subscriptions by logging in with Google. Your actual YouTube subscriptions appear here for easy access (Premium feature).

Managing subscriptions

• Subscribe / Unsubscribe -- Tap the button on any channel card to toggle your subscription.
• Channel bar -- Subscribed channels appear as a horizontal scrollable row at the top of your home feed, similar to YouTube's channel bar. Tap a channel avatar to see its videos.
• Channel detail -- Tap any channel card to view its detail page with the latest videos.
• Home feed -- Shows recommended videos from your subscribed channels, with pull-to-refresh support.

How to search

Tap the magnifying glass icon on the home page (Subscribe tab). Type your query and press search.

Search features

• Search history -- Up to 10 recent queries are saved locally. Tap a history item to re-search, or swipe to delete.
• Channel results -- Matching channels appear as horizontal scrollable circles at the top of the results.
• Video results -- Each result shows thumbnail, title, channel name, duration, and view count. Tap to open in Deja's player.
• Infinite scroll -- Scroll down to automatically load more results.

Advanced filters

Tap the filter icon for YouTube-style search filters:

• Content Type -- All, Video, Channel, Playlist, Movie
• Duration -- Any, Short (<4 min), Medium (4-20 min), Long (>20 min)
• Upload Date -- Any, Last hour, Today, This week, This month, This year
• Sort By -- Relevance, Upload date, View count, Rating
• Features -- Subtitles, Creative commons, HD, 4K, 360°, VR180, 3D, HDR, Location, Live

Active filters are indicated by a green filled icon.

How to import

1. Open the video in the Bilibili app or website
2. Tap the share button and copy the video link
3. In Deja, go to the Corpus tab, tap the + icon, and paste the link

On desktop, you can also use the Chrome Extension to import Bilibili videos with one click. If the video has no subtitles, use Deja Transcription or Local Transcription to generate them from the audio.

Cached audio

Bilibili videos provide cached audio for offline playback. This means during Deja Memory review, example sentences from Bilibili videos play the original speaker's voice at the exact timestamp -- no TTS fallback needed.

How to use

On the home page, tap the Deja logo in the top-left corner to switch between Video mode and Podcast mode. In podcast mode, you can search for podcasts, subscribe to series, and play episodes directly in Deja.

Podcast Subscriptions

Tap the + icon in Podcast mode to open the subscription management screen.

• Recommended podcasts -- Deja provides admin-curated podcast series for language learning. Each card shows cover art, series name, author, description, and a subscribe button.
• Subscribe / Unsubscribe -- Tap the button on any podcast card to toggle your subscription. Subscribed podcasts appear as a horizontal scrollable row at the top of your home feed.
• Drag to reorder -- Long-press and drag subscribed podcasts to customize the display order. Your custom order is saved locally.
• Episode feed -- The main feed shows recommended episodes from your subscribed podcasts with episode title, series name, duration, and publish date. Pull down to refresh.

Podcast Search

Tap the magnifying glass icon to search for any podcast series worldwide.

• Global database -- Deja's podcast database covers millions of series across all languages and genres.
• Search history -- Up to 10 recent queries are saved locally. Tap a history item to re-search, swipe to delete, or clear all.
• Search results -- Each result shows podcast cover art, series name, author, and episode count. Tap to open the podcast detail page.
• Podcast detail -- The detail page shows all episodes of a series. Subscribe to the series, browse episodes, and tap any episode to start playback with subtitle generation.

In this section

• Playback & Subtitles -- Audio playback, transcription options, caching, and learning features
• Listening Mode -- Focused listening practice with hide/reveal, translation, and grammar tools

Audio playback

Tap any episode to start playing. The player uses AVPlayer for native audio playback, providing reliable performance and background audio support. The episode cover art is displayed at the top, with the subtitle list below.

Generating subtitles

Most podcasts don't come with transcripts. Deja can generate high-quality subtitles using either:

• Deja Transcription (cloud) -- Uses server-side AI models for the best accuracy. Consumes quota based on audio duration. Works in the background.
• Local Transcription -- Uses on-device Whisper models. Free, but requires the app to stay open during processing.

For podcasts, Deja first downloads and caches the audio file, then sends it for transcription. This ensures reliable subtitle generation even for long episodes.

Audio caching

When transcribing a podcast, Deja automatically downloads and caches the audio file locally. Cached episodes can be played offline and are used for Deja Memory review audio playback.

Control bar

The podcast control bar is identical to the YouTube control bar, featuring:

• Progress bar -- Drag to seek within the episode.
• Previous / Next sentence -- Jump between subtitles for sentence-by-sentence study.
• Sentence loop -- Repeat the current sentence for intensive listening.
• Playback speed -- Adjust from 0.5x to 2x.
• Listening mode -- Switch to focused listening view.
• PDF export -- Export the full transcript as a printable PDF.

How to enter

Tap the headphone icon in the bottom control bar (available in both YouTube and Podcast players). The subtitle list is replaced by a single-sentence card view with a green border.

Hide / Reveal text

Tap the eye icon in the bottom-right corner to hide the subtitle text. This turns the card into a listening-only exercise. Tap again to reveal. In Settings, you can customize what to hide:

• Hide all -- Both original text and translation are hidden. The card shows skeleton placeholders.
• Hide original only -- The translation remains visible; the original text is replaced with skeleton lines. Good for testing if you can understand the spoken words.
• Hide translation only -- The original text is shown; the translation is hidden. Good for testing comprehension without relying on translation.

Listening mode tools

The bottom of the card provides quick-access buttons:

• Translate -- Tap the caption icon to get an AI translation of the current sentence. Useful when you can't understand what was said.
• Text selection -- Tap the cursor icon to enter selection mode. Select any part of the sentence to add it as a custom phrase.
• Grammar analysis -- Tap the magnifying glass icon to break down the sentence structure.
• Save sentence -- Tap the heart icon to save the current sentence to your corpus.
• Hide/Show -- Toggle text visibility with the eye icon.

Recommended workflow

1. Enter listening mode and hide the text
2. Listen to the sentence and try to understand it
3. Reveal the text to check your comprehension
4. Tap words you don't know to look them up
5. Use sentence loop to listen again until it feels natural
6. Save interesting sentences for flashcard review

How to access

Switch to Podcast mode by tapping the Deja logo on the home page, then tap the + icon to open "Manage Subscriptions".

Browse podcasts

• Recommended podcasts -- Admin-curated podcast series for language learning. Each card shows cover art, series name, author, description, and a subscribe button.
• Subscribe / Unsubscribe -- Tap the button on any podcast card to toggle your subscription.

Your subscriptions

• Podcast bar -- Subscribed podcasts appear as a horizontal scrollable row at the top of the Podcast home page. Tap a podcast avatar to see its episodes.
• Drag to reorder -- Long-press and drag to customize the display order. Your custom order is saved locally.
• Episode feed -- The main feed shows recommended episodes from your subscribed podcasts with episode title, series name, duration, and publish date.
• Pull to refresh -- Pull down to load new episodes from your subscribed podcasts.

How to search

In Podcast mode, tap the magnifying glass icon on the home page. Type your query and press search.

Search features

• Global database -- Deja's podcast database covers millions of series across all languages and genres.
• Search history -- Up to 10 recent queries are saved locally. Tap a history item to re-search, swipe to delete, or clear all.
• Search results -- Each result shows podcast cover art, series name, author, and episode count.
• Podcast detail -- Tap a result to open the detail page with all episodes. Subscribe to the series, browse episodes, and tap any episode to start playback with subtitle generation.
• Cached results -- Search results are cached locally for faster reloading.

Importing books

Import EPUB files from your device's local storage. The book opens in Deja's built-in reader with all learning features available.

Deja's EPUB reader is built on the Readium framework, providing a professional-grade reading experience with full support for EPUB standards. The reader automatically extracts the book's cover image, table of contents, and reading positions.

In this section

• Reading Experience -- Themes, fonts, reading modes, and advanced typography
• Controls & Navigation -- Floating action button, table of contents, search, bookmarks
• Text Interaction -- Snippet, Look Up, Highlight, and two learning modes
• Snippet Detail -- Phrase extraction, translation, grammar analysis, and more
• Highlights & Sync -- Visual highlight system and reading progress sync

• Reading modes -- Switch between scroll mode (continuous vertical scrolling) and page-turn mode (swipe to flip pages)
• Themes -- Three built-in themes: Deja (dark gray background with white text), Sepia (warm paper tone), and Dark (pure dark mode)
• Fonts -- Multiple font families including Serif, Sans Serif, OpenDyslexic (for dyslexia accessibility), IA Writer Duospace, and Accessible DfA
• Font size -- Adjustable text size to match your reading preference
• Progress tracking -- Page indicator shows your current position (e.g., "45 of 320") and overall reading progress percentage

Advanced typography settings

Fine-tune the reading layout through the Themes & Settings panel:

• Line height -- Adjust spacing between lines for comfortable reading
• Letter spacing -- Control the space between individual characters
• Word spacing -- Adjust the gap between words
• Page margins -- Set the amount of whitespace around the text
• Paragraph spacing -- Control the gap between paragraphs
• Hyphens -- Enable or disable automatic word hyphenation
• Column count -- Choose auto, single, or two-column layout
• Type scale -- Adjust the overall typographic scale

• Contents -- View the table of contents with your current progress. Tap any chapter to jump directly to it. The current chapter is highlighted.
• Annotations -- View all your highlights: saved snippets (green), phrases (orange), words (blue), and bookmarks. Tap any annotation to jump to its location.
• Search Book -- Full-text search within the entire book. Search results are highlighted in yellow when you jump to them.
• Learning Preferences -- Configure word/phrase tap behavior (Quick View vs Deep Learning), auto-highlight settings, and phrase highlight filters (by type, by CEFR level).
• Themes & Settings -- Adjust reading theme, font, text size, reading mode, and advanced typography settings.
• Add/Remove Bookmark -- Bookmark the current page for quick access later.

• Snippet -- Select a complete sentence (5+ words) and tap "Snippet" to save it as a learning segment. The passage is auto-saved with its location in the book, so you can always return to the original context.
• Look Up -- Select a single word or short phrase and tap "Look Up". Deja automatically finds the complete sentence containing your selection, then shows the word definition or phrase details.
• Highlight -- Select a word and tap "Highlight" to mark it with a blue underline without opening a detail sheet. This is useful for quickly marking vocabulary while reading without interrupting your flow.

You can also select an already-highlighted word and tap "Unhighlight" to remove the marking.

Two learning modes

In Learning Preferences, you can choose how word and phrase taps behave:

• Quick View -- Tapping a highlighted word or phrase shows a compact detail sheet directly over the reading view. You see the definition or phrase explanation without leaving the page. Best for casual reading when you want quick lookups.
• Deep Learning -- Tapping enters a full-screen Snippet detail view where you can look up words, extract phrases, translate the sentence, analyze grammar, and save the passage. Best for intensive study sessions.

• Phrases -- AI extracts idioms, phrasal verbs, and collocations from the sentence. Extracted phrases are highlighted in the text and can be tapped for details.
• Translate -- Get a context-aware AI translation of the entire passage.
• Select -- Enter manual phrase selection mode: tap words to build a custom phrase that the AI didn't automatically identify.
• Grammar -- Break down the sentence into grammatical components with color-coded visualization.
• Favorite -- Save the snippet to your corpus. Favorited snippets appear as green highlights in the book and become flashcards for spaced repetition review.

You can enable auto-translate and auto-extract phrases in the settings (via the "..." button in the top-right corner) so these features run automatically every time you create a new snippet.

• Green background -- Saved snippets (favorited sentences). These passages are part of your corpus and will appear in Deja Memory review.
• Orange underline -- Extracted phrases. Tap any orange-underlined text to see the phrase definition, category, and CEFR level.
• Blue underline -- Highlighted words. These are vocabulary items you've marked during reading.

In Learning Preferences, you can filter phrase highlights by type (phrasal verb, idiom, collocation, etc.) and by CEFR level (A1/A2, B1/B2, C1/C2), or turn highlights on/off entirely.

Reading progress sync

When you open a book from your bookshelf, Deja automatically syncs your reading position to the cloud. When you return to the book later -- even on a different device -- you'll resume exactly where you left off. All saved snippets, word highlights, and phrase annotations are also synced across devices.

If you have videos downloaded on your device (e.g., lectures, interviews, movie clips), you can import them directly into Deja. The video will be processed locally and subtitles can be generated using Deja Transcription or Local Transcription.

This is especially useful for content that isn't available on YouTube or Bilibili.

Subtitle options

• Deja Transcription -- Server-side AI transcription with high accuracy. Consumes quota.
• Local Transcription -- On-device Whisper models. Free, but the app must stay open.
• SRT / ASS import -- If you already have subtitle files (.srt or .ass), you can import them directly. This is useful when you have professional transcripts or fan-made subtitles.

How to import

1. Open the TikTok app and find a video you want to learn from
2. Tap the share button and copy the video link
3. In Deja (iOS), go to the Corpus tab
4. Tap the + icon and paste the TikTok link

Deja will process the video link and generate subtitles using Deja Transcription for learning. Note: Deja does not download TikTok videos -- it extracts the audio for transcription.

Supported content

TikTok import works great for short-form language learning content: vocabulary tips, grammar explanations, pronunciation practice, cultural context, and everyday conversations. Since TikTok videos are short, they're perfect for focused learning sessions.

Why subtitles matter

In Deja, subtitles aren't just text on screen -- they're the infrastructure that powers word lookup, phrase extraction, grammar analysis, translation, and flashcard review. High-quality subtitles mean better learning outcomes.

Subtitle sources

• Platform subtitles -- Fetched directly from YouTube or Bilibili. Fast but may contain recognition errors or poor segmentation.
• Deja Transcription -- Server-side AI transcription with high accuracy, natural sentence breaks, and proper punctuation. Consumes quota.
• Local Transcription -- On-device Whisper models. Free, no quota needed, but requires the app to stay open.
• SRT / ASS import -- Import external subtitle files for local videos. Useful when you have professional transcripts or fan-made subtitles.

Why re-transcribe?

Even when a video has existing subtitles, many learners choose to re-transcribe because:

• Auto-generated subtitles often have recognition errors
• Sentence segmentation may be unnatural, making phrase extraction less effective
• Punctuation and capitalization may be incorrect
• Re-transcribed subtitles better support word frequency tracking, phrase identification, and grammar analysis

Subtitle Interactions

Each subtitle in the video player supports swipe gestures for quick actions:

Swipe Left

• Save sentence -- Tap the heart icon to save the subtitle to your Sentence Collection. A filled heart indicates it's already saved.
• Edit subtitle -- Tap the pencil icon to modify the subtitle's original text or translation. Useful for correcting transcription errors or adding your own translation.
• Copy subtitle -- Tap the copy icon to copy the subtitle text to your clipboard.

Swipe Right

• Grammar analysis -- Swipe right to trigger Grammar Analysis for the selected subtitle. Full swipe activates it instantly.

Tap Actions

• Tap a subtitle -- Jumps the video to that subtitle's timestamp and starts playback from there.
• Tap a word -- Opens the Word Lookup panel with definitions, examples, and the option to save the word.
• Tap a highlighted phrase -- Opens the Phrase Detail panel with meaning, usage, and examples.

What affects accuracy

• Audio quality -- Unclear audio, heavy background music, noise, or multiple overlapping speakers will reduce accuracy regardless of which transcription method you use.
• Transcription model -- Three local models: Aether (fastest, least accurate), Stratus (balanced), Nimbus (slowest, most accurate).
• Deja Transcription -- Cloud AI achieves the highest accuracy (~99.8%), but is still affected by poor audio quality.

Tips for better results

• Choose content with clear speech and minimal background noise
• Use Nimbus model for local transcription when accuracy matters most
• Use Deja Transcription for the highest quality subtitles
• Edit subtitles manually if you spot errors (swipe left on iOS)

How it works

Deja Transcription uses professional AI models running on our servers. The audio is processed in the cloud, producing subtitles with high accuracy, natural sentence breaks, and proper punctuation.

• Works in the background -- you can close the app and come back later
• Supports multi-language detection
• Consumes quota based on audio duration (approximately 0.2 quota per minute)

Transcription modes

Free users cannot use Deja Transcription. Local Transcription (on-device Whisper) is available to everyone at no cost. See Plans & Pricing for details.

Available models

Advantages

• No quota consumption
• Works offline (after model download)
• Audio stays on your device -- fully private

Looking up words

While watching a video, listening to a podcast, or reading a book, tap any word in the subtitle or text to see its definition. Deja provides:

• Context definition -- AI analyzes the word's meaning in the current sentence, not just generic dictionary entries
• Full definitions -- All common meanings are listed below the context definition
• Context sentence -- Tap to replay the original audio where the word appeared
• Context source -- Tap to jump back to the original video, podcast, or book location

Saving words

Tap the heart icon in the lookup window to save the word to your corpus. Every saved word automatically tracks:

• All sentences where it appeared — across ALL content sources
• The video/podcast/book source for each occurrence, grouped by source
• Frequency count across all your content

Saved words are also highlighted in subtitles and book text across all your content, so you can see them in different contexts and reinforce your memory naturally.

Word Family

Deja introduces the Word Family concept: a single word entry automatically includes all its common forms -- noun, verb, adjective, adverb. For example, looking up "create" also shows "creation", "creative", "creatively", and "creator".

This design makes vocabulary learning more systematic and three-dimensional, closer to how language is actually used in real contexts.

Lookup modes

You can customize the lookup behavior in Settings:

• Tap to look up -- Tap any word in the current subtitle to immediately open the lookup window
• Long press to look up -- Tap to play the sentence, long press to look up the word

Word settings

• Word highlighting -- Saved words are highlighted in subtitles so you can track your progress
• Show detailed definitions -- Toggle between compact and expanded definition views
• Auto Deja Definition -- When enabled, context-aware AI definition loads automatically on lookup

Automatic extraction

As you play a video, listen to a podcast, or read a book, Deja automatically identifies phrases in each subtitle or text, including:

• Phrasal verbs -- e.g., "look forward to", "break down"
• Idioms -- e.g., "a piece of cake", "hit the nail on the head"
• Collocations -- e.g., "make a decision", "take advantage of"
• Prepositional phrases -- e.g., "in terms of", "on behalf of"

Auto phrase extraction consumes 0.05 quota per sentence.

Manual selection

In listening mode, tap the phrase button, then manually select the text range you want to add as a phrase. This is useful when you spot an expression that the AI didn't automatically identify.

Phrase details

Tap any phrase to see:

• The phrase in its original context
• Base form of the phrase
• Definition and explanation
• Category (phrasal verb, idiom, etc.) and CEFR level

Tap the heart icon to save the phrase to your corpus for flashcard review.

Phrase highlighting

In Settings, you can customize phrase highlighting:

• Toggle phrase highlights on/off
• Filter by phrase type (different colors for each type)
• Filter by CEFR level (A1/A2, B1/B2, C1/C2)

How to save sentences

• Videos/Podcasts: Swipe left on a subtitle and tap the heart icon to save it
• In listening mode, tap the heart icon to save the current sentence
• Books: Select text in the EPUB reader, tap Snippet, then Favorite to save
• Edit -- You can edit subtitle text if the transcription contains errors before saving

What gets saved

Each saved sentence records:

• The exact text, timestamp (video) or page location (book)
• The source video/podcast/book
• Audio playback link for video sources (uses cached audio or TTS)

Sentences from all sources (YouTube, Bilibili, Podcast, TikTok, Local Video, EPUB Books) are unified in Deja Memory flashcards.

Explore this section

• Structured Analysis -- Color-coded sentence structure breakdown with interactive highlights
• Key Phrases -- Automatic identification of idioms, collocations, and fixed expressions with CEFR levels
• Where to Use -- Access grammar analysis from videos, podcasts, books, and flashcards

How to access

• Swipe right on a subtitle to enter grammar analysis mode
• In listening mode, tap the magnifying glass icon
• In book reading, tap the grammar button in the Snippet view
• In Deja Memory, sentence cards display cached grammar analysis on the back if available

Sentence Type Recognition

The AI first identifies the overall sentence type -- simple, compound, complex, or compound-complex. This label appears at the top of the analysis view, giving you an immediate overview of the sentence's structure.

Sentence Structure Breakdown

The original sentence is displayed with each structural component highlighted in a different color:

• Main clause -- The core statement of the sentence
• Subordinate clauses -- Dependent clauses such as conditional (if...), temporal (when...), causal (because...), etc.
• Exclamatory sentences, relative clauses, adverbial phrases, and other modifiers

Colors cycle through light blue, yellow, orange, and coral red to ensure clear visual distinction between components, even in long sentences with many parts.

Interactive Highlights

Tap any colored text segment to reveal its detail card:

• Component type -- e.g., "Main clause", "Conditional adverbial clause"
• Explanation -- A concise description of what this part of the sentence does
• Grammar point -- The core grammar rule demonstrated by this structure (e.g., "if-clause uses present tense for future conditions")

A "tap colored text" hint appears when no component is selected, guiding first-time users.

Caching & Auto-save

Grammar analysis results are automatically cached on the server. If you open the same sentence again, the cached result loads instantly instead of re-analyzing. When you close the analysis sheet, any edits are automatically saved.

Phrase Types

The AI identifies and categorizes phrases into five types:

• Collocations -- Words that commonly go together (e.g., "make a decision", "heavy rain")
• Phrasal verbs -- Verb + particle combinations that create new meanings (e.g., "break down", "look forward to")
• Prepositional phrases -- Preposition-based expressions (e.g., "in terms of", "on behalf of")
• Idioms -- Figurative expressions (e.g., "a piece of cake", "hit the nail on the head")
• Fixed expressions -- Standard phrases with set forms (e.g., "as a matter of fact", "to be honest")

Phrase Cards

Each identified phrase is displayed as a card showing:

• Standard form -- The base form of the phrase (e.g., "take a break")
• Original form -- How it actually appears in the sentence (e.g., "taking a break"), shown when different from the standard form
• Meaning -- Definition in your native language
• Type tag -- Collocation, phrasal verb, idiom, etc., with a matching icon
• CEFR difficulty -- Color-coded level tag from light green (A1/A2) to deep green (C1/C2)

Saving Phrases

Tap the heart icon on any phrase card to save it to your corpus. Saved phrases:

• Are added to your personal corpus for review
• Are highlighted in subtitles across all your content
• Track their source sentence, video/book, and timestamp

The phrase section is collapsible -- tap the header to expand or collapse it. Your preference is remembered across sessions.

Videos (YouTube, Bilibili, Local)

In the subtitle list, swipe right on any subtitle to open grammar analysis. The analysis is linked to the subtitle ID, so results are cached on the server and load instantly when you open the same subtitle again.

Podcasts

Same as videos -- swipe right on any podcast subtitle. In listening mode, tap the magnifying glass icon to analyze the currently playing sentence.

Books / EPUB

In the Snippet Detail view (after tapping a sentence in a book), tap the grammar button to analyze it. Book grammar analysis stores results per document segment, and phrases saved from books include the exact reading location (locator) for easy navigation back.

Deja Memory (Flashcards)

Sentence-type flashcards display cached grammar analysis on the card back if it has been previously generated. You can tap the grammar button to open the full analysis sheet, review the sentence structure, and save any new phrases you discover during review.

Native Language Support

Grammar explanations and phrase meanings are generated in your native language setting. The AI adapts its explanations to be most useful for speakers of your language -- for example, highlighting grammar patterns that are particularly challenging for Chinese speakers learning English, or vice versa.

Unlike traditional machine translation that processes each sentence in isolation, Deja's AI translation analyzes the surrounding context to produce more accurate and natural translations.

• Translation language follows your native language setting
• You can manually edit both the original text and the translation
• Consumes 0.02 quota per sentence

How it works

Every word, phrase, and sentence you save in Deja automatically becomes a review card. The FSRS (Free Spaced Repetition Scheduler) algorithm determines when each card should be reviewed based on your memory feedback.

• Cards you remember well get longer intervals
• Cards you struggle with appear more frequently
• Each review happens in context -- you see the original sentence and can play the original audio

Context Recall

Deja Memory is designed around Context Recall -- not just recalling a word's meaning, but re-experiencing the language in its original context. When you see a phrase during review, you can instantly recall:

• Which video or podcast it appeared in
• The speaker's tone and expression style
• The overall logic and structure of the sentence

When memory is bound to context, review becomes more efficient. Each review is a context revisit, not mechanical repetition.

Explore this section

• Card Types -- Word, phrase, and sentence cards with unique front/back layouts
• Review & Rating -- FSRS scheduling, rating buttons, card states, and smart audio playback
• Settings & Stats -- Daily quotas, auto-pronunciation, notifications, and learning statistics

Entry page

The Deja Memory tab shows a grid with three cards -- Words, Phrases, and Sentences. Tap any card to start a review session for that type. A chart icon in the top-right corner opens your learning statistics.

Word cards

Word cards focus on individual vocabulary in context.

• Front -- The word in large text, phonetic transcription (for English), a pronunciation button, and up to 2 example sentences with play buttons. No translation is shown on the front.
• Back -- Full definition with color-coded part-of-speech tags (n. adj. v. etc.), up to 3 example sentences with translations, context-specific meanings you can tap to expand, and links to jump back to the source video or book.
• Word detail -- Tap the word text to open its full detail page with all saved contexts, synonyms, and usage history.

Phrase cards

Phrase cards use cloze deletion (fill-in-the-blank) for active recall.

• Front -- The original sentence with the phrase replaced by underscores (e.g., "I need to ___ ___ ___ my schedule"). Optionally shows the Chinese definition if enabled in settings.
• Back -- The phrase revealed with its definition, the full original sentence, and a link to the source content. Audio playback is available for the example sentence.

Sentence cards

Sentence cards test comprehension of complete sentences.

• Front -- The Chinese translation of the sentence. Your task is to recall the original English sentence.
• Back -- The original sentence with audio playback, a link to the source video/podcast, and cached grammar analysis (if previously generated) showing color-coded sentence structure.

Card interactions

• Tap to flip -- Tap anywhere on the front of the card to reveal the answer.
• Pronunciation -- Tap the speaker icon to hear the word or phrase. Word cards use dictionary audio for English; other languages use TTS.
• Jump to source -- Tap an example sentence to open the original video or book at the exact position.
• Context meaning -- Word cards show how the word is used in each specific context, with a detailed explanation you can tap to expand.
• Grammar analysis -- Sentence cards include grammar breakdown if available, showing sentence structure with color-coded components.
• Word detail -- Tap the word text on a word card to open its full detail page with all saved contexts, synonyms, and usage history.

FSRS scheduling

After viewing the answer, rate your recall with one of four buttons:

• Again -- Didn't remember at all. The card will reappear in about 1 minute.
• Hard -- Remembered with difficulty. Short interval (minutes to hours).
• Good -- Remembered correctly. Standard interval growth.
• Easy -- Remembered instantly. Large interval jump (days to weeks).

Each button shows the predicted next review time, calculated by the FSRS algorithm based on the card's history. This ensures front-end and back-end scheduling stay perfectly in sync.

Graduation logic

New cards start in the Learning phase with short intervals (minutes). After reviewing a card at least twice and rating it Good or Easy, the card graduates to the Review phase with day-level intervals. This mirrors Anki's learning steps (1min → 10min → graduate) but is managed by FSRS for optimal scheduling.

Learn-ahead window

Cards due within the learn-ahead limit (default 20 minutes) are included in your current session. This keeps learning flow uninterrupted -- if a card is due in 5 minutes, you'll see it now instead of ending your session early. You can adjust this window from 5 to 60 minutes in settings.

Card states

Each card goes through a lifecycle managed by FSRS:

• New (blue) -- A freshly created card that hasn't been reviewed yet.
• Learning (orange) -- A card in the initial learning phase with short intervals.
• Review (green) -- A graduated card on a regular review schedule (days to months).
• Relearning (red) -- A card you forgot during review, now back in short-interval learning.

The status badge in the top-left corner of each card shows its current state, and the difficulty badge in the top-right shows Easy/Medium/Hard based on your historical performance.

Smart audio playback

During review, every example sentence has a play button. Deja uses a smart audio priority system:

1. Podcast cache -- If the sentence came from a podcast episode you've transcribed, the cached audio is played at the exact timestamp.
2. YouTube cache -- If the sentence came from a YouTube video with cached audio, it plays the precise clip.
3. Bilibili / Local video -- Same approach for Bilibili cached audio or local video files.
4. TTS fallback -- If no cached audio is available, Deja uses text-to-speech with the correct language.

This means you hear the real speaker's voice during review, not a robotic TTS -- the exact sentence, at the exact moment, from the original content.

Session progress

During a review session, the top bar shows your progress as "completed / total". A card counts as completed only when its next due date is beyond the learn-ahead window. Cards still in the learning phase cycle back to the end of your queue until they graduate.

Review settings

Tap the gear icon during a review session to customize:

• Daily quota -- Set the number of new cards and review cards per day, separately for words, phrases, and sentences.
• Learn-ahead limit -- Cards due within this time window (default 20 minutes) will be shown in the current session instead of waiting.
• Word auto-pronunciation -- Toggle automatic pronunciation when a word card appears (front) or when you flip it (back).
• Phrase auto-pronunciation -- Toggle automatic TTS for the phrase when a phrase card appears or is flipped.
• Show meaning on front -- For phrase cards, optionally show the Chinese definition on the front alongside the cloze sentence.
• Review reminders -- Enable daily notifications at a custom time to remind you to review.

Daily quota details

Each card type has its own independent quotas:

• Words -- Default: 10 new cards, 100 review cards per day
• Phrases -- Default: 5 new cards, 50 review cards per day
• Sentences -- Default: 5 new cards, 50 review cards per day

New cards are shown first, followed by review cards ordered by due date. Settings are synced to the server and shared across devices.

Learning statistics

Tap the chart icon to view your learning progress:

• Today's overview -- Due reviews, cards reviewed, new cards learned, and a progress bar.
• Accuracy rate -- Percentage of cards rated Good or Easy.
• Average interval -- How many days on average between reviews, indicating long-term retention.
• Card type distribution -- Breakdown of your cards by words, phrases, and sentences.

Session complete

When all cards in a session are finished, a summary screen shows your total cards reviewed and accuracy rate for the session. From here you can view detailed statistics or return to the entry page.

If you prefer using Anki for spaced repetition, you can export your saved items from the web dashboard:

• Export words with definitions and example sentences
• Export phrases with context and explanations
• Export sentences with translations

The export generates standard Anki-compatible files that can be imported directly into the Anki desktop or mobile app.

Payment methods

• iOS -- Apple In-App Purchase
• Android -- Google Play
• Web -- Stripe (credit card, supports CAD and CNY)

Manage subscription

You can cancel your subscription anytime. After cancellation, your plan remains active until the current billing period ends. Manage your subscription in:

• iOS -- Settings > Apple ID > Subscriptions
• Android -- Google Play > Subscriptions
• Web -- Account settings on the pricing page

What is quota?

Deja quota is the credit unit for AI-powered features. Different features consume different amounts:

Quota by plan

• Free -- 50 quota (one-time, does not renew)
• Premium -- 500 quota per month
• Ultra -- 1,000 quota per month
• Lifetime -- Same monthly quota, but unused quota accumulates across months

Free features (no quota needed)

• Fetching existing platform subtitles
• Local transcription (on-device Whisper)
• Word lookup (basic dictionary)
• Flashcard review
• Saving words/sentences/phrases

Share your referral code with friends. When they sign up using your code, both you and your friend receive bonus quota. The more people you invite, the more quota you earn.

Find your referral code in the app's profile section or on the web dashboard.

Deja automatically caches content to your device for offline access and faster loading. Cached files stay on your device until you manually delete them.

What Gets Cached

Why Cache?

• Offline access -- Read books, listen to podcasts, and review content without internet.
• Faster loading -- No need to re-download content you've already accessed.
• Flashcard audio -- Cached audio powers playback during Deja Memory review sessions.
• Background listening -- Cached podcast episodes can be played in Listening Mode without buffering.

Managing Cache

You can manage your cached files from the app's settings:

• Podcast cache -- View and delete individual episode caches or clear all podcast audio at once.
• Whisper models -- Download, switch, or delete Local Transcription models.
• Books -- Deleting a book from your library also removes its local cache.

Deja can sync your local files across all your Apple devices using iCloud. When enabled, your books, podcasts, and video audio are automatically kept in sync.

Enabling iCloud Sync

1. Open the app and go to Profile > Settings
2. Find the iCloud Sync toggle and turn it on
3. Make sure you're signed into iCloud on your device

The sync status indicator shows the current state: syncing, last sync time, or error details.

What Gets Synced

Files are synced in two categories:

Visible in Files App (iCloud Drive)

These files appear in the Files app under iCloud Drive > DejaVocab:

• EPUB books -- Your imported EPUB files
• Podcast audio -- Cached podcast episodes
• Local videos -- Imported local video files

Private (Background Sync)

These are synced to a private iCloud container (not visible in Files app):

• YouTube audio cache -- Extracted audio tracks
• Bilibili audio cache -- Extracted audio tracks

Not Synced

• Whisper models -- Too large; download separately on each device via Local Transcription settings
• Image cache -- Thumbnails and cover art (re-generated automatically)
• Temporary files -- Processing artifacts

When Does Sync Happen?

Sync is triggered automatically at these moments:

• App launch -- Checks for new files from other devices
• Returning from background -- Syncs when you switch back to Deja
• Every 5 minutes -- Periodic background sync while the app is open
• After saving content -- Importing a book, caching a podcast, etc.
• Entering background -- Pushes local changes before the app sleeps

How It Works

• Upload -- New or modified local files are uploaded to iCloud.
• Download -- Files found in iCloud but missing locally are downloaded.
• Conflict resolution -- The newer file (by modification date) takes priority.
• Delete sync -- Deleting a book or podcast cache also removes it from iCloud.

Reading Position Sync

Your reading position in EPUB books is synced via the Deja server (not iCloud). When you close a book, your position is saved to the cloud. Opening the same book on another device will resume from where you left off.

Troubleshooting

• "iCloud login required" -- Sign into iCloud in your device's Settings > Apple ID.
• Sync failed -- Check your internet connection and iCloud storage space.
• Files not appearing on another device -- Make sure iCloud Sync is enabled on both devices and wait a few minutes.
• Large files syncing slowly -- EPUB and podcast files can be large. Sync happens in the background; check the status indicator in Settings.