AI Summarizer: 7 Tools for Text, PDFs, Video, and Audio

The best AI summarizer depends on what you are summarizing. A pasted paragraph, a 40 page research paper, a two hour YouTube lecture and a recorded meeting are four different problems, and most tools are built for one or two of them. Pick the tool by its input first, then by how much it lets you check the result.

This guide compares seven AI summarizer tools by the sources they accept, what their free tiers actually allow, and where each one breaks. You will also see what independent research says about summary accuracy, because a fast summary that drops the key finding costs you more time than reading the original.

Our Top Picks at a Glance

How We Evaluated These AI Summarizer Tools

Four criteria shaped the ranking, and they matter more than any marketing claim about speed.

Input range. A summarizer that only accepts pasted text forces you to copy, convert and clean before you even start. Tools that read a PDF, a link or a recording directly remove that friction, and the friction is usually where people give up.

Length limits. Free tiers cap you by words, files or minutes. A 1,200 word cap is fine for an article and useless for a textbook chapter. We report the published limits so you can match them to your material.

Verifiability. A summary you cannot trace back to the source is a summary you have to trust blindly. Tools that cite passages, keep a transcript beside the summary, or let you ask follow-up questions make checking practical.

What happens after the summary. For study and work, a summary is rarely the end. Turning it into flashcards, a quiz, an email or a translated version decides whether the tool saves time or just moves the work.

#1 Top Pick: Primo Notes

Primo Notes is an AI note taking app for iOS and Android that turns almost any input into a structured note, and summarizing is one of the tools you run on that note. It takes eight kinds of input: a voice recording, audio shared in from another app such as a WhatsApp voice note, a photo of handwritten or printed pages, a PDF, DOCX or PPTX file, a YouTube link, a web page URL, and plain text.

Why it ranks first. Most summarizers make you choose the tool by the source. A lecture goes to one app, the slides to another, the reading to a third. Here every source becomes the same kind of note, with a title, a structured body and a formatted transcript, so the summary of a lecture and the summary of its slides sit side by side in one place.

Key features for summarizing

Recordings are transcribed in 101 languages with automatic language detection, and anything with more than one voice comes back with speaker labels, so a group discussion is summarized as a conversation rather than a wall of text. Summarize is one of seven tools on a finished note, next to rewrite, translate, quiz, flashcards, mind map and follow-up email. Rewrite lets you shorten or simplify a summary further and set the formality level.

Ask AI is a chat over a single note, which is how you check a summary: ask where a claim came from, and the answer draws on that note rather than on the open web. Feynman mode goes a step further and has you explain the material out loud while the app works the gaps.

Limitations

It is mobile only. There is no web app or desktop version, so if your workflow lives entirely in a browser on a laptop, a browser tool fits better. It also summarizes one note at a time rather than synthesizing across a library of dozens of sources, which is where NotebookLM is stronger.

Ideal for: students who record lectures and photograph handouts, and professionals who need meetings, documents and links summarized in the same place. If you only want a quick result without installing anything, the free PDF summary tool on the website runs in the browser with no account.

#2: NotebookLM

NotebookLM is Google's free research assistant, built on Gemini, and it answers only from the sources you add. That grounding is its strongest feature: every answer carries inline citations back to the passage it came from, so you can verify a summary line by line instead of taking it on faith.

It accepts PDFs, Google Docs and Slides, web pages, YouTube videos through their transcripts, audio files, Word documents and plain text. On the free tier a notebook holds up to 50 sources, with up to about 500,000 words per source, which is more than most coursework or project research will ever need. The Studio panel turns those sources into study guides, FAQs, quizzes, flashcards and the podcast style Audio Overviews it is known for.

Why choose it. When the job is to summarize across many sources at once, such as ten papers for a literature review, NotebookLM is the best fit on this list. You can ask how two sources disagree, which is something a single document summarizer cannot do.

Drawbacks. Diagrams, charts and equation images are read with limited fidelity, so it is weaker on math and science material where meaning sits in figures. Reviewers also report that caveats buried in the middle of long documents are often skipped in its audio summaries, a pattern discussed further below. And it works best on a computer; capturing a lecture live is not what it is built for.

#3: ChatGPT

ChatGPT is the most flexible option because you control the summary with your prompt. Ask for five bullet points, a one paragraph abstract, the methodology only, or a version a 12 year old could follow, and it adapts.

According to OpenAI's help center, files uploaded to a conversation can be up to 512 MB, and text documents are capped at 2 million tokens per file. That limit is generous enough for most books. The constraint on the free tier is frequency: free users can upload 3 files per day, which rules it out for heavy daily use without a paid plan.

Why choose it. You already know how to use it, and it handles odd formats and odd requests well. Summarizing a contract into plain language, then asking which clauses carry risk, is a natural two step conversation.

Drawbacks. It does not cite passages by default the way NotebookLM does, so checking a summary means going back to the file yourself. It is also a general assistant, which means it has no built-in flashcard deck or quiz history; anything you build from the summary lives in a chat thread you will have to find again.

#4: QuillBot Summarizer

QuillBot's Summarizer is the simplest tool here: paste or upload text, optionally pick keywords to focus on, and choose paragraph or bullet point output. It works well for articles, essays and single chapters.

The limits are published clearly. According to the QuillBot help center, the free plan summarizes up to 1,200 words per input and Premium raises that to 6,000 words. Custom mode, where you describe the summary you want, is part of Premium.

Why choose it. For a quick summary of a short text, nothing on this list is faster. QuillBot also suggests using the Summarizer on your own writing: if the summary misses your main point, your draft probably does too. That is a genuinely useful editing check.

Drawbacks. At 1,200 words, the free tier cannot handle a full research paper, which often runs well past that. It does not take video or audio, and the result is plain text with nothing built on top of it.

#5: Scholarcy

Scholarcy is built specifically for academic reading. It is trained to pick out the key terms, claims and findings of a research paper, and it turns them into what it calls Summary Flashcards: a structured card per paper with highlighted findings rather than a single paragraph.

It reads PDFs, book chapters, online articles, plain text and YouTube videos, and you can import by drag and drop, by URL, or through a browser extension. The free summarizer covers 3 articles a day and exports flashcards one at a time.

Why choose it. If your main material is journal articles, a summary organized around findings and evidence is more useful than a generic overview. It is the closest thing on this list to a reading assistant designed by people who read papers for a living.

Drawbacks. Three summaries a day is tight during a heavy research week, and saving unlimited summaries needs a paid plan. Outside academic text it has little advantage over a general tool.

#6: NoteGPT

NoteGPT started as an AI video summarizer and still leads with YouTube. Paste a link and it pulls the transcript and produces a summary, and it can summarize a whole playlist or batch up to 20 videos at once. NoteGPT says it places no limit on video length and can handle videos without subtitles. It also accepts audio, PDFs, images, web pages and long text.

Why choose it. For anyone who learns from YouTube lectures and tutorials, batch summarizing a playlist turns a weekend of watching into an hour of reading. It works in the browser with no install.

Drawbacks. A video summary is only as good as the transcript under it, and automatic captions on technical lectures often garble terminology. Treat the summary as a map of where to look in the video, not a replacement for the parts that matter. For a single video, the YouTube summarizer comparison on this blog covers more options in depth.

#7: Otter.ai

Otter.ai is a meeting tool first. It records live conversations through its apps, can join scheduled calls on the major video platforms, and imports audio or video files up to 5 GB. Once a recording is transcribed, it generates a summary, action items and an outline.

The free Basic plan is the most restrictive on this list for summarizing recordings. Its free plan limits are 300 transcription minutes a month, 30 minutes per conversation, and 3 imported files per account in total, not per month. Anything past the 30 minute mark of a recording stays locked until you upgrade.

Why choose it. If your summaries are mostly of team meetings, Otter's meeting integrations and action items fit that job well, and its connector to ChatGPT lets you query past meetings from there.

Drawbacks. A 30 minute cap cuts most lectures in half, and three lifetime imports make it impractical for summarizing recordings you already have. It is not built for documents or video links at all.

Which AI Summarizer Fits Which Source

The rankings above describe each tool on its own. In practice you face a specific source on a specific day, so here is how the choice plays out for four common cases.

A 90 minute lecture

Otter's free tier stops at 30 minutes per conversation, which leaves two thirds of the lecture locked. A video summarizer only helps if the lecture is on YouTube. For a live lecture you record yourself, you need an app that records without a length problem, transcribes, and summarizes the transcript afterwards. Recording on your phone also captures what the slides leave out: the examples, the asides, and the "this will be on the exam" moments.

A 30 page research paper

QuillBot's 1,200 word free cap covers roughly the abstract and introduction, not the paper. Scholarcy is designed for exactly this case and organizes the summary around claims and findings. If you have several papers on the same question, add them all to one NotebookLM notebook and ask where they agree, which no single document summarizer can answer.

A YouTube course

A playlist of 15 videos is where batch summarizing pays off. NoteGPT's batch mode handles up to 20 videos at once, and NotebookLM can pull in each video's transcript as a source you can question later. Either way, check technical terms against the video, since automatic captions are the weak link.

A team meeting

Meeting summaries need speaker labels and action items more than elegant prose. Otter is built for this inside a company that standardizes on it. For in-person meetings or a one-off call, a phone recording with speaker diarization gives you the same structure without inviting a bot into the room, and a follow-up email drafted from the note closes the loop.

How Accurate Are AI Summaries?

Every tool above can produce a confident summary that is wrong, and the research on this is consistent.

When the BBC tested four major assistants on its own news articles, it found that AI chatbots inaccurately summarized the content: 51% of answers had significant issues, and 19% of answers citing BBC content introduced factual errors such as wrong numbers and dates. A follow-up led by the BBC and coordinated by the European Broadcasting Union scaled the test to 22 public broadcasters in 18 countries and 14 languages. That EBU report found that 45% of more than 3,000 responses contained at least one significant issue, with sourcing problems the most common.

Why Long Documents Are Riskier

A widely cited Stanford-led study, titled Lost in the Middle, showed that language models use information at the start and end of a long input far better than information in the middle. Performance dropped significantly when the relevant detail sat mid-document. For a summary of a long paper or a two hour lecture, the caveat on page 14 is exactly what gets lost.

How to Reduce the Risk

Three habits reduce the risk:

• Check the numbers. Every figure, date and name in a summary should be confirmed against the source, because these are the details models get wrong most often.
• Summarize in sections. Split a long document or recording into parts and summarize each, so nothing sits in a vulnerable middle.
• Ask, then verify. Use a tool that answers follow-up questions from the source, such as NotebookLM's citations or Ask AI on a note, and look up anything that surprises you.

What to Look for in an AI Summarizer

If none of the seven fits exactly, these are the questions that separate a useful AI summarizer from a frustrating one.

Does it take your source directly?

Converting a video to text or a photo to a PDF before you can summarize it adds steps you will skip under pressure. Check that the tool reads your most common source as is, whether that is a recording, a link or a scanned page.

Do the free limits match your material?

Compare the cap to a real example of what you summarize. A free tier measured in 1,200 words, 3 files a day or 30 minutes per recording can be fine or useless depending on whether you summarize articles, papers or lectures.

Can you trace the summary back?

Look for citations, a transcript beside the summary, or a chat that answers from the source. Without one of these, checking accuracy means rereading the original, which defeats the purpose.

Does it work in your language?

An AI summarizer that handles only English is a real limit for international students and multilingual teams. Look for automatic language detection and translation if your sources come in more than one language.

What can you build from the summary?

For studying, the summary is the start of review, not the end. Flashcards, quizzes and the ability to shorten or simplify the summary decide whether it becomes study material or just sits in a folder. For a manual approach that sharpens your own summarizing, the guide on how to summarize anything by hand pairs well with any of these tools.

Conclusion

Match the AI summarizer to the source. QuillBot is quickest for short text, Scholarcy reads research papers best, NoteGPT handles YouTube in bulk, Otter fits team meetings, ChatGPT is the most flexible, and NotebookLM is strongest when you need to summarize across many sources with citations.

Whichever tool you use, treat the summary as a draft. Independent research shows nearly half of AI answers about news content contain a significant issue, and details in the middle of long inputs are the most likely to disappear. Summarize in sections, confirm every number, and use the summary to find what matters in the original rather than to replace it.