# Phosphor > Slug: `notetube-ai` · Platforms: **Android** · Category: Productivity ## Meta - Title: Spaced Repetition App: FSRS Cards From Lectures | Phosphor - Tagline: Spaced repetition with FSRS: turn a lecture video, a topic or your own notes into flashcards, and review each card on the day you would forget it. ## Short description Phosphor is a spaced repetition app that builds flashcards from a lecture video, a topic or text you paste, then schedules each card with FSRS for the day you would forget it. Your decks export to Anki at any time. ## Long description Phosphor is a spaced repetition app for people who study from lectures. Paste a video link, type a topic or paste notes you already have, and Phosphor writes a summary and notes, then builds flashcards from them. Every card from a video links back to the second it came from. Each card is scheduled with FSRS. You grade yourself Again, Hard, Good or Easy, and the next review lands on the day your chance of remembering falls to the target: 90% by default, 95% in the last 14 days before an exam date you set. Cards you keep missing collect in their own list so you can rewrite, reset or suspend them. A due card can show up as a notification with its question, and you can grade it right there. Quizzes, cloze cards, concept maps, confusable-pair drills, free recall and teach-it-back mix up how you are tested. Export any deck to Anki (.apkg or CSV), Markdown for Obsidian or PDF. ## Official URLs - Landing: https://apps.teamzlab.com/notetube-ai/ - Google Play: https://play.google.com/store/apps/details?id=com.teamzlab.notetube_ai - Android package: `com.teamzlab.notetube_ai` ## SEO keywords - spaced repetition - spaced repetition app - ai flashcards - flashcard app - youtube video summarizer - youtube video to notes ## Hero - Headline: Spaced repetition that brings each card back before you forget it - Subheadline: Turn a lecture video, a topic or your own notes into flashcards. FSRS schedules every card for the day it starts to fade, and a reminder brings it back. There is a free plan to start with. - Primary CTA: Get it on Google Play - Secondary CTA: How it works ## Screenshot captions - screenshots/1.webp: Phosphor flashcard review showing a sample card fading from 99% memory on day 0 to 18% on day 12 - screenshots/2.webp: Phosphor deck screen with 10 saved flashcards, every card linked to its source, plus Review and Quiz buttons - screenshots/3.webp: AI-written summary of a physics lecture on Newton's laws, shown before the questions - screenshots/4.webp: Flashcard question and answer about shunt direction across a VSD, with a 100% retention score - screenshots/5.webp: Forgetting curve panel flagging 2 flashcards slipping below 30% retention for review - screenshots/6.webp: Review complete screen: 18 flashcards reviewed, all caught up for today ## Feature blocks ### FSRS spaced repetition Every card is scheduled with FSRS-6. Grade it Again, Hard, Good or Easy and the next review lands on the day your chance of remembering drops to 90%. Hard cards come back sooner, easy ones wait longer. ### An exam date that changes the schedule Add the date of your exam and, in the last 14 days before it, the target rises to 95% recall, so reviews come closer together exactly when it matters. ### Flashcards from a lecture video Paste a video link and Phosphor writes a summary, notes and 10 flashcards from the captions (25 on Pro). Each card links to the second it came from: tap the timestamp and the player jumps there. ### Or from a topic, or your own notes Type a topic and Phosphor writes study notes on it first. Or paste a handout, lecture notes or a chapter you typed up, and the cards are built from that text. ### Review from the notification When a card is due, the reminder shows the question with Again, Hard, Good and Easy buttons. Tap a grade and Phosphor opens with that grade already applied — no deck to find, no second tap. ### Different ways to be tested Chapter quizzes, cloze (fill-in-the-blank) cards, concept maps, confusable-pair drills, free recall and teach-it-back. A card you only ever see in one form gets easy to recognise long before you really know it. ### Fix the cards you keep missing Cards that keep failing collect in one list, Cards you keep missing, where you can rewrite, reset or suspend them instead of grinding the same bad card for weeks. ### Your cards stay yours Export any deck as a native Anki package (.apkg), an Anki CSV, Markdown for Obsidian or a PDF, or add the review schedule to your calendar. Notion sync is part of Pro. ## How it works ### Step 1: Start from a video, a topic or your notes Paste a lecture link, type a topic, or paste text you already have. Phosphor writes a summary and notes first. ### Step 2: Keep the cards you want Flashcards are built from the notes. Check a video card against its timestamp, then save it to a deck. ### Step 3: Review on the day it fades FSRS sets each card's next date from your grade. A reminder brings due cards back, and you can grade a card straight from the notification. ## FAQ ### Q: What is the best spaced repetition app? It depends on whether you want to write your own cards. Anki is the most configurable and has the biggest shared decks. Phosphor suits people who study from lectures and want the cards built for them: it makes flashcards from a video, a topic or pasted notes and schedules each one with FSRS. It exports to Anki, so you are not locked in. ### Q: What is FSRS in spaced repetition? FSRS (Free Spaced Repetition Scheduler) is an open-source scheduling algorithm. It estimates how stable each memory is and how hard the card is for you, then predicts the day your chance of recalling it falls to a target. Phosphor uses FSRS-6 with a 90% target by default, raised to 95% in the 14 days before an exam date you set. ### Q: How does spaced repetition beat the forgetting curve? The forgetting curve falls fastest in the first days after you learn something. Each time you pull the answer back out of memory, the fall slows, so the next review can wait longer. Spaced repetition times each review for the point where you are close to forgetting, which is when recalling does the most good. Phosphor shows a retention estimate for each card so you can see the fade. ### Q: Can AI make flashcards from a YouTube video? Yes. Paste a lecture link and Phosphor reads the captions, writes a summary and notes, and builds 10 flashcards on the free plan, or 25 on Pro. Each card links to the second of the video it came from, so you can tap the timestamp and check it. If a video has no captions, you can paste an SRT or VTT transcript instead. ### Q: How often should I review flashcards? Let the schedule decide instead of a fixed rota. A new card comes back soon, then after longer and longer gaps as you keep getting it right, and a card you miss comes back quickly. In Phosphor you grade each card Again, Hard, Good or Easy and FSRS sets the next date from that grade. ### Q: Can I export my flashcards to Anki? Yes. Any deck exports as a native Anki package (.apkg) that imports in one tap, or as a tab-separated CSV. You can also export Markdown for Obsidian or a PDF, and add the review schedule to your calendar. ### Q: Is Phosphor free? There is a free plan: up to 10 video summaries and 3 new flashcard decks a week, and reviewing the cards you already have is not limited. Phosphor Pro raises them to 500 summaries and 100 decks a week, makes more cards per video and adds Notion sync. ### Q: Can I grade a flashcard from the notification? Yes. When a card is due, the reminder shows its question with Again, Hard, Good and Easy buttons. Tapping one opens Phosphor with that grade already applied, so the schedule updates the same way a review inside the app does, with no deck to find and no second tap. ## Store / monetization (from content; verify on store) - Price: free - In-app purchases: true --- ## Landing page body (full markdown below the fold on site) ## What a spaced repetition app does A spaced repetition app shows you each flashcard again just before you are likely to forget it, and waits longer every time you remember it. Phosphor is a spaced repetition app that schedules every card with FSRS and builds the cards for you from a lecture video, a topic you type, or notes you paste in. The idea is old. In the 1880s Hermann Ebbinghaus measured how fast he forgot lists he had learned and found that the loss is steep at first and then levels off: the forgetting curve. Each time you successfully pull a fact back out of memory, the curve flattens and the next review can wait longer. Rereading does far less than this. Recalling the answer before you see it is what does the work. So a good spaced repetition app has two jobs. It makes you recall rather than reread, and it works out the day each card is due so you never have to keep a calendar of what to revise. ## How Phosphor schedules each card Phosphor uses FSRS, the Free Spaced Repetition Scheduler, through the open-source fsrs package, which implements FSRS-6. After every card you grade yourself Again, Hard, Good or Easy, the same four buttons Anki uses, so the habit carries over if you are coming from there. FSRS keeps an estimate of how stable each memory is and how difficult the card is for you, and from those it predicts the day your chance of recalling the card falls to the target. That day is the due date. By default the target is 90% recall. If you add an exam date, the last 14 days before it are drilled harder: the target rises to 95%, so reviews come closer together exactly when it matters most. A card you grade Hard returns after a shorter gap; one you grade Easy is pushed further out. You can see the fade as well as trust it. Each card carries a retention estimate, and a forgetting curve panel flags the cards slipping lowest so you can review those first. Cards you have failed four or more times collect in a separate list called Cards you keep missing, where you can rewrite, reset or suspend them. A card that keeps failing is usually a badly written card, not a bad memory, and reviewing it one more time does not fix that. ## Where the cards come from You do not have to write the cards yourself. Phosphor starts from one of three things. - **A lecture video link.** Phosphor reads the video's captions and writes a summary, notes and a set of flashcards: 10 per video on the free plan, 25 on Pro. Every card is tied to the second of the video it came from. Tap the timestamp and the player jumps there, so checking a card takes seconds instead of a re-watch. - **A topic you type.** Type something like "Newton's laws of motion" and Phosphor writes study notes on it first, then builds cards from those notes. - **Text you already have.** Paste lecture notes, a handout or a chapter you typed up, and the cards are built from that text. If a video has no captions, Phosphor tells you so rather than guessing, and you can paste a transcript in SRT or VTT format to load the captions yourself. A playlist can become an ordered course with chapters, or one deck that you preview card by card, keeping or rejecting each before anything is saved. That means Phosphor also works as a YouTube video summarizer and a way to turn a YouTube video into notes. The summary is the start, not the product: notes you read once fade like anything else, and the cards are what you keep. We wrote up the longer version of how this works in [how AI turns YouTube lectures into Anki cards](/blog/youtube-to-flashcards-how-ai-turns-lectures-into-anki-cards/), and there is a walkthrough for [turning Boards and Beyond lectures into an Anki deck](/blog/boards-and-beyond-to-anki-free-tool/). ## Review from the notification A due card can reach you as a notification that shows its question, with four buttons underneath: Again, Hard, Good and Easy. Tap a grade and Phosphor opens with it already applied — the schedule updates the same way it would for a review inside the app, and you land on the next card instead of hunting for the deck. A two-minute review in a queue counts exactly as much as a review at your desk, and that is most of what keeps a deck alive through a busy week. ## Different ways to be tested A card you only ever see in one form gets easy to recognise long before you really know it, so Phosphor varies the format: - chapter quizzes with multiple choice, true or false and short answers - cloze cards, where you fill in the blank - concept maps that lay out the main ideas of a lecture in order - confusable-pair drills for two ideas you keep mixing up - free recall, where you write down everything you remember before you look - teach-it-back, where you explain the idea in your own words You can also put a question to one lecture or to your whole library, and the answer is drawn from your own notes with a timestamp pointing at where it came from. A weekly recap sums up what you covered. ## Your cards stay yours Export any deck whenever you like: as a native Anki package (.apkg) that imports in one tap, as a tab-separated CSV for Anki, as Markdown for Obsidian, or as a print-friendly PDF. You can also add the review schedule to your calendar. Notion sync, which pushes notes and cards into a Notion database you choose, is part of Pro. ## The free plan and Pro The free plan covers up to 10 video summaries and 3 new flashcard decks a week. Reviewing the cards you have already saved does not count against any limit, so a deck you built in September keeps working in December whether or not you pay. Phosphor Pro raises the limits to 500 summaries and 100 new decks a week, makes 25 cards per video instead of 10, and adds Notion sync. ## Who it is for, and when Anki is the better choice Phosphor fits students who revise from recorded lectures, in medicine and nursing, law, engineering or computer science, and language learners. It also suits anyone who got to the end of an online course and found that most of it had already gone. If you already have a large Anki deck tuned the way you like, and you enjoy writing your own cards, Anki is excellent and you may not need anything else. Phosphor is for getting from a lecture to a scheduled deck without that setup. Because every deck exports as an .apkg, moving your cards to Anki later costs you nothing. ## The same app, a new name Phosphor was formerly NoteTube AI. It is the same app under a new name. One part of the older app is still there for people who make videos rather than study them: Channel Radar. Track up to 3 channels on the free plan, or 50 on Pro. Their uploads are checked every 15 minutes, and when a new video gets twice that channel's usual views in its first 48 hours, you get a notification.