SubShadow
Learn Japanese from what you're already watching.
SubShadow turns the subtitles of your own media into study material. It follows whatever is playing on your Plex or Jellyfin server — or plays video straight from your phone. Tap any word for an instant definition with furigana, save it in one tap, and master it with built-in spaced repetition.
iPhone · Japanese → English · v1
Immersion without the friction
Everything between you and understanding — dictionaries, readings, flashcards — built into the subtitles themselves.
Tap to look up
Every subtitle word is tappable. An instant dictionary sheet shows the meaning, reading, and pronunciation — the show pauses while you read, resumes when you're done.
Furigana built in
Readings appear above every kanji, right in the transcript, so you never lose the thread of a line you can almost read.
It understands conjugation
Real dialogue isn't written in dictionary form. SubShadow deinflects what it sees — 遅れちゃった resolves to 遅れる — so the words people actually say are the words you can actually look up.
Mine words as you watch
One tap saves a word into your study deck with the sentence it appeared in — and, if you want, a still frame and a few seconds of audio from the line itself. You learn it in context instead of as a bare entry on a list.
Spaced repetition, built in
Saved words become flashcards scheduled by FSRS, the modern algorithm Anki offers. Decks, daily limits, suspend and bury, and both flashcard and quiz review modes — with statistics tracking what you've actually watched and reviewed.
Export to Anki — or don't
Nothing here is a walled garden. Send a deck to Anki as a .apkg with your
captured frames and audio inside it, dump your vocabulary as a .tsv, or back
up your words, decks and review history. Or just never leave the app.
Offline dictionary
The full Japanese–English dictionary ships inside the app: over 217,000 entries, with JLPT levels marked where they apply. Lookups are instant and need no internet connection at all.
Bring your own video
Browse and play your Plex or Jellyfin library in the app, or shadow what's already playing on your TV. No server? Send files to your phone from your computer's browser over Wi‑Fi, or drop them in with the Files app.
Private by design
No accounts, no sign-up, no sync. Your saved words, decks, and review history stay on your device, and nothing about your library or your watch history is ever uploaded to us. A subtitle search you start sends the title to the service you picked. Read the privacy policy.
How it works
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Connect
Point SubShadow at your Plex or Jellyfin server, or put video on the phone itself — over Wi‑Fi from your computer's browser, or with the Files app. Or start with Demo mode: a bundled Japanese scene to read along with and look words up in, with no server and no sign-up.
Plex Jellyfin On this iPhone — Wi‑Fi or Files Demo — free, no server
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Watch
Play in the app, or let SubShadow shadow what's already running on your TV — either way you get a scrolling, tappable transcript with the readings above the kanji.
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Study
Tap words you don't know, save the ones worth keeping, and review them later in short, scheduled sessions — rate how well you recalled each one and SubShadow decides when you next need to see it.
Pricing
The free tier is fully functional. Pro removes the card cap and unlocks in-app playback of your Plex or Jellyfin library.
| Feature | Free | Pro |
|---|---|---|
| Tap-to-look-up & furigana | ✓ | ✓ |
| Demo mode | ✓ | ✓ |
| Spaced-repetition reviews | ✓ | ✓ |
| Saved cards | 20 | Unlimited |
| Play demo & on-device video in the app | ✓ | ✓ |
| Play your Plex or Jellyfin library in the app | — | ✓ |
| Subtitle download & sync (Jimaku · OpenSubtitles) | ✓ | ✓ |
| Export to Anki, TSV, or a backup file | ✓ | ✓ |
Pro Monthly
$9.99 / month
Auto-renewing subscription.
Pro Annual
$47.99 / year
Includes a 7-day free trial. Auto-renewing subscription.
Lifetime
$89.99 one-time
Pay once, keep Pro forever.
Purchases are made inside the app on the App Store. Payment is charged to your Apple Account at confirmation of purchase. Subscriptions automatically renew unless cancelled at least 24 hours before the end of the current period; your account is charged for renewal within 24 hours prior to the end of the current period. You can manage or cancel your subscription in your Apple Account settings after purchase. Any unused portion of a free trial is forfeited when you purchase a subscription. See the Terms of Use (EULA) and the Privacy Policy.
Frequently asked questions
Do I need a Plex or Jellyfin server?
No — twice over. Demo mode runs a bundled Japanese scene fully offline, with no server and no sign-up: a live transcript on Now Playing, and the clip itself on Watch. And you can put your own video straight on the phone: open the Wi‑Fi transfer screen and send files from your computer's browser, or drop them into SubShadow's folder with the Files app. Both play in the app with the same interactive transcript. A server is only needed if you already have one and want to use the library on it.
Can SubShadow pause and rewind what's playing on my TV?
On most players, yes — tapping a word pauses the show while you read it, and there's a replay-this-line button and a scrubber. This works through Plex's Companion protocol (or Jellyfin's remote-control API), which every proper Plex or Jellyfin app speaks: Apple TV, Android TV, the smart-TV apps, the desktop app, the mobile apps.
The exception is Plex Web — Plex played in a browser tab. It doesn't implement Companion, so no app can drive it. SubShadow detects this and greys out play/pause, replay and the scrubber rather than firing commands into a void, with a note saying why. Everything else still works: the transcript follows along, and tapping a word still looks it up — the video just keeps rolling while you read. If you want the pause, play through a Plex app instead of the browser, or play the episode inside SubShadow.
Which languages are supported?
Japanese → English. That's the whole of it today, and it's what the app is built and tuned for — the conjugation handling, the readings, the JLPT tagging. Other languages are possible (the architecture keeps each one behind a swappable dictionary pack), but nothing else is promised or scheduled. If there's a language you'd use this for, say so at support@subshadow.app — that's what would decide it.
What video formats can I put on the phone?
MP4, M4V and MOV play directly. MKV is converted on import — the container is rewritten without re-encoding the video, so it's quick and the picture is untouched. AAC and Dolby audio is copied as-is; Opus and FLAC audio, which MP4 can't carry, is converted to AAC. A few files can't be made to play on an iPhone at all (10-bit anime encodes are the usual culprit — no Apple device has a hardware decoder for them); SubShadow tells you which file, why, and the exact command that fixes it, rather than failing silently.
Is there an iPad or Mac version?
Version 1 is iPhone-only.
Does SubShadow upload my media or watch history?
No. There are no accounts and no sync, so there is nowhere for it to go — your video, your subtitles, your saved words, and what you watched all stay on the device. The only thing that leaves on its own is anonymous, aggregate usage analytics (via the EU-hosted TelemetryDeck), which you can turn off in Settings, plus a small configuration file the app fetches at launch that carries nothing about you. Searching for subtitles sends the title of what you're watching to the subtitle service you picked — but only when you start a search. Full details are in the privacy policy.
Where do subtitles come from?
From the subtitle tracks already on your server or in your own files. When there isn't one, SubShadow can search and download a matching Japanese subtitle without leaving the player, from Jimaku (anime and Japanese TV — you paste your own free API key) or OpenSubtitles (live-action TV and film — no key needed, signing in is optional and only raises your daily download limit). Downloading subtitles is free, not a Pro feature, and there's a built-in offset control for fixing sync.
Does the dictionary need an internet connection?
No — the full Japanese–English dictionary is bundled inside the app, so lookups work offline and are instant.
How do I cancel a subscription or get a refund?
Subscriptions are managed in your Apple Account settings (Settings → your name → Subscriptions on iPhone). Refunds are handled by Apple at reportaproblem.apple.com.