InterSub

Dual subtitles and a pop-up dictionary inside Netflix and YouTube.

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Screenshot of InterSub, Dual subtitles and a pop-up dictionary inside Netflix and YouTube

What is InterSub?

InterSub is a browser extension for Chrome, Edge and Firefox that adds dual subtitles and a hover dictionary to Netflix, YouTube, Prime Video and course platforms, saving looked-up words to a Wordbook with Anki and Telegram practice.

InterSub is a browser extension that overlays two subtitle tracks on streaming video and course platforms: the original language and a translation into the viewer's native tongue. It works on Netflix, YouTube, Prime Video, HBO Max, Crunchyroll, Bilibili.tv, TED, Coursera, Udemy, LinkedIn Learning, Domestika, DW Learn German, Learn.cantrill.io and Shahid. The premise is simple: instead of carving out separate study time, learners pick up vocabulary while watching the shows and lectures they already consume. The core interaction is the pop-up dictionary. Hovering any word in the subtitle pauses the video and opens a card with an AI-generated definition and a context translation for the surrounding phrase, so idioms and phrasal verbs are explained as whole units rather than word by word. Every lookup is filed into a Wordbook with the original sentence, and that list can be exported to Excel or synced with Anki. A Telegram bot adds spaced repetition practice, resurfacing saved words just before they would be forgotten. An AI Language Buddy, built on ChatGPT, answers questions about grammar or cultural references without leaving the episode. InterSub is aimed at intermediate learners who can follow a plot but stall on slang, and at beginners who want the safety net of a native-language line. It also suits heritage speakers and mixed-language households. The feature set goes beyond translation: subtitles can be hidden during playback and shown only on pause, shadowing mode stops after each line for repetition, and hotkeys resize or reposition the text. A Remote Control feature turns a phone into a playback and lookup remote via a QR code, though the product itself remains a desktop extension. Among alternatives, InterSub sits closest to Language Reactor and Immersive Translate, but its emphasis is on the loop from watching to saving to drilling, rather than on subtitle display alone. AI subtitle translation is reserved for paid plans; the free tier keeps dual subtitles with a monthly cap on lookups.

How do you use InterSub?

  1. 1Install the extension for your browser
    Open the install page and add InterSub from the Chrome Web Store, Microsoft Edge Add-ons or Firefox Add-ons. Chromium browsers such as Brave and Arc use the Chrome build.
  2. 2Set your language pair
    In the extension settings, choose the language you are learning under Translate from and your native language under Translate to. Dozens of pairs are supported, including English to Japanese and German to English.
  3. 3Open a video and check the dual subtitles
    Start an episode on Netflix, YouTube or a course platform. Two lines should appear, the original above and the translation below. Use the hotkeys to resize or reposition them if they cover the picture.
  4. 4Hover a word to look it up
    Hover any word in the subtitle line. The video pauses and a pop-up shows an AI definition plus a translation of the surrounding phrase. The word is saved to your Wordbook automatically.
  5. 5Review saved words in the Dashboard
    Open Dashboard from the extension settings, then Words in the side menu, to see everything you have looked up. From there you can sync the list to Anki or export it to Excel.
  6. 6Practice with the Telegram bot
    Connect your Wordbook to the InterSub Telegram bot to train saved words with spaced repetition. The bot schedules each word for review just before you would forget it.

Pros and cons

Pros

  • Dual subtitles work across a wide set of streaming and course platforms, not just Netflix.AI
  • Hover lookup pauses the video and gives a context-aware definition, which helps with idioms and phrasal verbs.AI
  • Every lookup is saved with its sentence and can be synced to Anki or exported to Excel.AI
  • Telegram bot adds spaced repetition practice without a separate app.AI
  • Shadowing mode and pause-only subtitles support listening and speaking drills.AI

Cons

  • It is a desktop browser extension only; there is no native mobile app for watching inside.AI
  • An internet connection is required for translations and subtitle sync, so offline study is not possible.AI
  • AI subtitle translation for missing tracks is locked to paid plans.AI
  • The free plan caps word lookups per month, which heavy users will hit quickly.AI
  • Platform support depends on each site's subtitle implementation and can break when a streaming service changes its player.AI

How much does InterSub cost?

Free trial

Every new account gets a 14-day free trial of Premium. After the trial, the account stays on the free plan with dual subtitles and a monthly lookup cap.

Learn more

Pricing

Dual subtitles are free with a monthly limit on word lookups. Pay-as-you-go and Premium plans add more lookups and AI subtitle translation. Prices are not listed on the homepage; see the plans and prices page for current rates.

Learn more

Support

Help is provided through an FAQ on the homepage and a how-to page covering platform support and setup. No dedicated support portal or email is listed on the homepage.

Integrations

Works with Netflix, YouTube, Prime Video, HBO Max, Crunchyroll, Bilibili.tv, TED, Coursera, Udemy, LinkedIn Learning, Domestika, DW Learn German, Learn.cantrill.io and Shahid. Saved words sync with Anki and can be practiced in the InterSub Telegram bot or exported to Excel.

Features

Dual subtitles on Netflix, YouTube, Prime Video, HBO Max, Crunchyroll, Bilibili.tv, TED and course platforms; hover pop-up dictionary with AI definitions and context translation; automatic Wordbook with Anki sync and Excel export; AI subtitle translation for missing tracks; AI Language Buddy for grammar and cultural questions; shadowing mode, pause-only subtitles and hotkey controls; phone Remote Control via QR code.

Frequently asked questions about InterSub

  • How much does InterSub cost?
    Dual subtitles are free with a monthly limit on word lookups. Pay-as-you-go and Premium plans add more lookups and AI subtitle translation. Prices are not listed on the homepage; see the plans and prices page for current rates.
  • Does InterSub offer a free trial?
    Every new account gets a 14-day free trial of Premium. After the trial, the account stays on the free plan with dual subtitles and a monthly lookup cap.
  • How do you use InterSub?
    The walkthrough on this page covers 6 steps: 1. Install the extension for your browser 2. Set your language pair 3. Open a video and check the dual subtitles 4. Hover a word to look it up 5. Review saved words in the Dashboard 6. Practice with the Telegram bot.
  • What platforms does InterSub support?
    InterSub is available on Browser extension.
  • What does InterSub integrate with?
    Works with Netflix, YouTube, Prime Video, HBO Max, Crunchyroll, Bilibili.tv, TED, Coursera, Udemy, LinkedIn Learning, Domestika, DW Learn German, Learn.cantrill.io and Shahid. Saved words sync with Anki and can be practiced in the InterSub Telegram bot or exported to Excel.
  • What are the limitations of InterSub?
    It is a desktop browser extension only; there is no native mobile app for watching inside. An internet connection is required for translations and subtitle sync, so offline study is not possible. AI subtitle translation for missing tracks is locked to paid plans.

Status

StatusActive
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Added10/21/2026

Platforms

Browser extension

Pricing

FreemiumFree TrialSubscription

Categories

Language LearningLearningVideo TranslationEducationTranslation