MP4 to MP3

Why doing this locally is the point

Audio extraction is one of the most common things people want from a video and one of the most awkward to hand over. A lecture recording, an interview, a therapy session recorded with consent, a voice memo captured on video, a rehearsal take: all of them are private in a way that a holiday clip is not, and all of them end up on some website's server the moment you use a typical online extractor.

Here the video never moves. FFmpeg compiled to WebAssembly runs in your browser tab, reads the file from your own disk and writes the MP3 back to it. Nothing about the recording becomes part of a network request, which is a property you can check rather than a promise you have to accept.

What extraction actually does to the audio

The audio inside a video file is already compressed, usually as AAC. Extracting it to MP3 decodes that and encodes again with a different lossy codec, so this is a second pass rather than a copy. Nothing is recovered and a small amount is given up.

For speech, which is most of what people extract, this is inaudible and irrelevant. For music you care about it is worth knowing that a compressed video is a poor source: if a lossless or higher quality original exists anywhere, extract from that instead. And the extraction is the whole audio track, from the first frame to the last. Trimming needs a timeline, which this page does not have.

The first run, and what stops it working

The first extraction downloads a single WebAssembly build of FFmpeg, about 30 MB, served from this domain and cached by your browser afterwards. It is fetched only when you convert, never on page load, so opening this page costs you nothing.

The real constraint after that is your device's memory, because the file is decoded inside the browser tab. A two hour recording at high bitrate is where this starts to strain, and a phone gives up sooner than a laptop. There is no number to quote, because the limit depends on your hardware and on what else you have open. If an extraction fails on a phone, try the same file on a desktop browser before assuming anything is wrong with it.

Does this keep the video?

No. It extracts only the audio and saves it as an MP3. The video is discarded.

What video formats work?

Most common formats including MP4, MOV, WebM and MKV.

Does extracting audio lose quality?

A little. The audio in the video is already compressed, and encoding it to MP3 compresses it a second time. It is fine for speech, podcasts and lectures. For music you care about, extracting from a lossless source is always better than extracting from a compressed video.

Is the video uploaded to convert the audio?

No. FFmpeg compiled to WebAssembly runs inside your browser, so the video is read from your own disk and never becomes part of a network request. Disconnect from the internet and it still works.

Why does the first extraction take so long?

The first run downloads the conversion engine, a single WebAssembly file of about 30 MB, and your browser caches it afterwards. Everything after that starts immediately.

Can I extract just part of a video?

Not on this page, which converts the whole audio track. Trimming needs a tool with a timeline, and desktop FFmpeg does it in one command.

Is it legal to extract audio from a video?

From your own recordings, yes. From material someone else owns, that depends entirely on the copyright and on the terms you agreed to, and this page cannot advise you on it.