A lecture summarizer for long YouTube lectures and your own recordings
Claras is a lecture summarizer for YouTube links and recordings you upload. You get chapters, the key takeaways and a full transcript you can search, so you can see what a lecture covers and find the part you need.
Why long lectures are hard to revise from
A lecture runs an hour or more. Your notes from the room have gaps where you were listening instead of writing, and the recording is 90 minutes you don't have time to sit through again. Speeding it up still means watching all of it, and scrubbing back and forth to find the ten minutes you didn't follow.
The same goes for lecture series on YouTube. A course of twelve one-hour talks is easy to save and hard to get through before an exam.
What Claras does with a lecture
Claras works from what you already have: a YouTube link, or a recording you made yourself. It reads the whole transcript and gives you chapters, the key takeaways, a section by section summary and a transcript you can search. You still decide what to study. You just stop guessing where it is.
It's an AI lecture summarizer, not a live note taker. It doesn't sit in your class or record it. If you're comparing those kinds of tools, our guide to choosing a lecture note taking app covers the difference.
Two ways in: a link or a recording
You need a free account, with no card. A YouTube lecture goes in as a link. A recording from your phone, laptop or a class video goes in as a file.
- Sign in, then paste a YouTube lecture link, or open the Video or Audio tab and choose your recording.
- Pick the language for your summary, one of 15. Claras remembers it.
- Press Analyze with AI. A long recording shows its progress as a percentage.
- Start with the chapters, then read the key takeaways, then search the transcript for what you need.
A worked example: a 90-minute recorded lecture
Say you recorded a 90-minute lecture on your phone, saved as an M4A file, and you want lecture recording to notes you can revise from by the weekend. This is what happens, step by step.
Before it starts
Claras reads the length of the file from its headers and checks your transcription hours. This lecture needs 1.5 hours. The free plan includes 1 hour every 30 days, so Claras tells you how many hours you have left instead of starting a job it can't finish. On Pro (10 hours) or Unlimited (100 hours) it goes ahead.
While it transcribes
Your browser reads only the audio out of the file and cuts it into slices of a few minutes, with a few seconds of overlap so a sentence at a cut isn't lost. The slices go to an AI transcription service four at a time, and the button shows the progress as a percentage. The first slice works out the language, and the rest use it.
Because the file is longer than 30 minutes, Claras offers to email you when it's done. Keep the tab open while it works. If it closes, choose the same file again and it continues from where it stopped, so you don't pay twice for the part already done.
When the summary is written
The transcript is read in 20-minute stretches, so a 90-minute lecture is read in five parts, each in full. Claras writes chapters as it goes, with at least one every five minutes or so, and each chapter gets a title and a one-line description. Then it writes a short opening, 4 to 8 key takeaways, and a summary of each section.
Turning it into notes
- Read the opening and the key takeaways to see what the lecture covered.
- Look down the chapters for the parts you didn't follow. Click one and your recording plays from that moment, from your own disk.
- Search the transcript for a term. Search matches part of a word, which helps when a technical term is spelled oddly.
- Ask narrow questions in Ask AI, like "Where does she explain the second example?"
- Download the summary and the transcript as text files, or copy them into your notes app.
The same lecture on YouTube
If the lecture is on YouTube with captions, Claras uses the captions instead. Nothing comes out of your hours, there's no upload to wait for, and the chapters jump to that moment in the YouTube player.
What you get from one lecture
- Chapters. A titled chapter at least every five minutes or so, each with a one-line description. On YouTube and on uploaded files, a click plays the lecture from that point.
- A summary. A short opening on what the lecture covers, 4 to 8 key takeaways that name specific points, then a section for each stretch of the lecture with headings and key terms in bold.
- The transcript. Every spoken line with its timestamp. Search it, copy it with or without timestamps, or download it as a text file or .srt subtitles.
- Ask AI. Questions answered from the transcript, usually with the time it came from. Claras also suggests three questions for each lecture.
- History. Each lecture is saved, so you can reopen the summary and transcript later in the term without running it again. An uploaded file isn't kept, so pick it again if you want to play it.
Make the summary fit how you study
In Settings you can write custom summary instructions, up to 500 characters, like "define each new term" or "write this as revision notes with short bullets". They apply to every summary you run after that. If you want to turn a lecture into notes in another tool, Send to AI copies the transcript and opens Claude, ChatGPT, Gemini, Gemini Notebook or Perplexity.
Tips for better lecture notes
Set your instructions first
Custom instructions shape the next summary you run, not ones already written. Set them before a busy week of lectures, then leave them.
Use the chapters as your outline
Copy the chapters into your notes and fill in under each one. It's quicker than starting from a blank page, and every heading has a time you can go back to.
Ask in the lecturer's words
Ask AI picks the parts of the transcript that share the most words with your question. If the lecturer says "heart attack", asking about "myocardial infarction" won't find it. Words of one or two letters are ignored, so spell out abbreviations. If Ask AI misses something, search the transcript and reuse the wording you find.
Run a series in one go
For a YouTube lecture series in a public playlist, Bulk Summaries works through the videos together, and you can choose one summary per video. In a batch, a summary of a long lecture may not read to the very end, so run the lectures that matter most on their own, where the summary covers the whole transcript. The free plan includes one Bulk Summaries run of up to 20 videos.
Record so it can be heard
A phone near the speaker beats one at the back of the room. Questions from the audience are often too faint to transcribe, so if one matters, note the time and listen to it yourself.
Name the file before you upload
The file name becomes the title in your History, so "Week 4 Cell Biology" beats "Recording 37".
Limits to know about
AI summaries can be wrong
An error can come from three places. The transcript can mishear a term, a name or a number. The AI can misstate a point, merge two points or drop a condition. And Claras doesn't know whether the lecture itself is right or up to date. Check anything you'll rely on against the recording and your course material.
It hears, it doesn't see
Claras works from spoken words. Slides, equations, diagrams and anything written on the board aren't in the transcript unless the lecturer says them aloud.
Plan limits
Each lecture counts as one of your videos: 3 a month on the free plan. Uploaded recordings also use transcription hours, 1 on the free plan, 10 on Pro and 100 on Unlimited over a rolling 30 days, with up to 6 hours per file. The pricing page has the details.
Other things that won't work
- Claras can't log in to your school's lecture portal or read a link behind a login. If you're allowed to download a recording, upload the file. Check your school's rules and your lecturer's wishes about recording first.
- The transcript doesn't say who is speaking, so a student's question and the lecturer's answer run together.
- Times in Ask AI answers are plain text, not links. Move the player there yourself, or click the matching chapter.
Your recording
The file itself isn't stored. Its audio is sent in slices to an outside AI transcription service set up not to keep it, and the transcript and summary are saved to your History.
Related
Compare plans to see how many hours each one includes.
Questions about summarizing lectures
Is there a free lecture summarizer here?
Yes. The free plan gives you 3 videos a month with no card. YouTube lectures with captions don't use any transcription hours, however long they are. Recordings you upload use hours, and the free plan includes 1 hour every 30 days.
Can I summarize a lecture I recorded on my phone?
Yes. Upload the file in the Audio or Video tab. Phone voice recorders usually save M4A or MP3, and both work, as do WAV, FLAC, MP4, MOV and a few more. If you want to test the transcription on a short clip first, the free voice memo to text tool takes a file up to 4 MB with no account and shows the first 10 minutes.
How long can a lecture be?
An uploaded recording can run up to 6 hours, as long as you have that many transcription hours left. A YouTube lecture with captions has no hours cost. A YouTube lecture with no captions needs AI transcription: up to 30 minutes on the free plan and up to 3 hours on a paid plan.
Does it work for lectures in other languages?
Yes. The transcript stays in the language of the captions or the recording, and the summary, chapter titles and Ask AI answers come back in the language you pick, one of 15. So you can read a summary in English of a lecture given in Spanish.
Can Claras record my lecture while it happens?
No. Claras doesn't record, join a class or transcribe live. Record the lecture with your phone or laptop first, where that's allowed, then upload the file.
Will this improve my grades?
We can't promise that, and we have no results to show you. What it does is turn a long lecture into chapters, takeaways and a transcript you can search, so you can see what was covered and find the parts you need to rewatch.
How accurate is an AI lecture summary?
It can be wrong. The transcript can mishear a term or a number, the AI can misstate or merge points, and it can't tell whether the lecture itself is correct. Use the summary to find your way around, then check anything you'll rely on against the recording and your course material.
Can it make flashcards or quizzes?
There's no flashcard or quiz feature. You can use Send to AI to take the transcript to Claude or ChatGPT and make your own there, then check the cards against the lecture.
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