Free browser tool
Turn an MP4 into an MP3
Drop an MP4 in and keep only the sound. It converts in this tab, on your own machine, with no upload and no queue.
- No sign up
- Nothing uploaded
- No queue
- Up to 300 MB a file
Drop a MP4 in
Drag a file onto this panel or open one. It is converted to MP3 in this tab, on your own machine, and never uploaded.
What is actually inside an MP4
An MP4 is a box with two things in it: a video track, almost always H.264, and an audio track, almost always AAC. Converting one to MP3 means throwing the first away and re-encoding the second. That is why a 400 MB recording of an hour long call comes back at around 25 MB, and why it takes seconds rather than minutes: nothing has to touch the picture.
It runs here, not on a server
This page is ffmpeg compiled to WebAssembly. Your MP4 is read off your disk by the browser, decoded in the tab and written back to your downloads folder. No upload, no queue, no link in an email, and no server that has a copy of your file for a fortnight.
The cost is a 32 MB download of the encoder, once per visit. After that every file starts immediately.
192 kbps
The MP3 is written at 192 kbps at whatever sample rate the MP4 carried. For a call, a lecture, a podcast or a screen recording that is past the point where more bitrate changes anything audible, and it keeps an hour under 30 MB.
It is a second lossy pass, because the AAC in the MP4 was already compressed. On speech that is inaudible. On music you intend to master, keep the original and work from it.
If you keep doing this
Pulling audio back out of a finished video is a repair. Prequel records your Mac's screen with the microphone and the system audio as separate tracks with separate gains, so the sound is already its own file before you start editing, and a notification over your voice is a slider rather than a re-record.
How it works
Converting in 3 steps
- Drop the MP4 inDrag it onto the panel or open a file. Up to 300 MB, which is a couple of hours of a screen recording.
- ConvertThe AAC audio inside the MP4 is decoded and written out as a 192 kbps MP3, on your own processor.
- DownloadThe MP3 keeps the MP4's name, so a folder of converted files still tells you which is which.
What it does
Free, and still worth using
Lose the picture, keep the sound
An MP4 is usually H.264 video next to AAC audio. The video track is dropped and the audio is re-encoded, which is why a 400 MB screen recording becomes a 20 MB MP3.
Convert without handing over the file
The conversion is ffmpeg compiled to WebAssembly, running in this tab. No server sees the MP4, which matters when it is a client call or an internal demo.
Get a file anything will play
MP3 at 192 kbps opens in every player, every car, every podcast app and every editor, which is the only reason to convert an MP4 that already plays everywhere.
Convert as many as you like
No daily cap, no sign up, no email for a link. The encoder loads once and every file after it starts immediately.
On a Mac, the editing is already done
Prequel records your screen at its full resolution, then opens an editor with the zooms already placed, your camera framed and a background applied. Export one MP4 at up to 4K.
No credit card required
- Zooms placed on every click
- Camera shaped, sized and framed
- Background, padding and shadow
- Microphone and system on separate gains
- Cursor smoothed and resized
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Old AVI in, H.264 MP4 out, converted on your own machine.
FAQ
Sound, size and privacy
Does this upload my MP4 anywhere?
No. The page runs ffmpeg inside your browser, so the MP4 is read from your disk, converted on your own processor and written back to your downloads folder. Nothing is sent to a server at any point.
How much smaller is the MP3?
Usually ten to twenty times. An MP4 spends almost all of its bytes on the picture, so a 400 MB recording of a one hour call lands around 20 to 25 MB as audio at 192 kbps.
Will the audio sound worse?
Slightly, and not audibly on speech. The AAC inside your MP4 is decoded and re-encoded as MP3 at 192 kbps, which is a second lossy pass; for a call, a lecture or a screen recording it is inaudible. For music you are mastering, keep the original.
Can I keep the original quality instead?
Convert to WAV if you need the decoded audio with nothing thrown away, or keep the MP4 itself. The file on your disk is untouched by this page either way.
What if my MP4 has no sound?
The run stops and the page says so. A screen recording made without a microphone or system audio has no audio track at all, so there is nothing to extract.
How long does it take?
About as long as it takes to read the file, plus a one-off 32 MB download of the encoder on your first conversion. An hour of audio is a minute or two on a current laptop.
Does it work on a phone?
Yes, on a modern iPhone or Android browser, with a smaller file. A phone has less memory to spare for the encoder, so stay well under the 300 MB ceiling there.
Can Prequel record the audio separately in the first place?
Yes. Prequel records your microphone and your Mac's system audio as separate tracks with separate gains, so you never have to pull one back out of a finished video.