Can this convert a video without uploading it?

Yes. The MP4 is read and decoded in your browser, and only its audio track is encoded. No file bytes leave this device.

What if the MP4 has multiple audio tracks?

The page lists the available tracks with their codecs and channels so you can choose one before converting.

MP4 to MP3 Converter

Choose an MP4 with an audio track and this page extracts that soundtrack locally, then encodes it as an MP3. The video stays untouched, and the file is never uploaded.

Open a MP4 file

· or drop one anywhere on the stage

Never uploadedNo accountUp to 50 MBUp to 10 minutes

From

Bitrate

Sample rate

Channels

Download

Ready. Choose a MP4 file, or drop one on the stage.

Audio tracks are listed before extraction, the video is never decoded, and a file with no audio track is refused. The output is a constant bitrate MP3 at the bitrate you choose, which is a lossy encode of what came in.

What the bytes sayread from the first bytes of the file, never from its extension
Open a file and its container is identified before anything is decoded.
Output sizeexact arithmetic for PCM, an estimate for MP3
Open a file to size the output.
Decoderasked of this browser before a conversion starts
A codec with no decoder here is named up front, not halfway through.

The From control is a mode, not a guess: the first bytes of the file are read and checked against it, so a file that was renamed is refused with what it actually is. An MP4 has its audio tracks listed before anything is extracted and its video is never decoded. Changing the sample rate resamples by linear interpolation, and changing the channel count averages a stereo pair down or copies a mono channel to both sides. The ceilings are 50 MB and 10 minutes, because the whole track is held as 32-bit samples in the memory of this tab before a single output byte is written.

Converting cannot restore what a lossy file already lost. Files are decoded and re-encoded in your browser, so nothing is uploaded. Converting cannot restore detail a lossy file already lost: MP3 to WAV makes a larger file, not a better one. Which formats can be decoded depends on your browser, and this page checks the file's actual bytes and its codec before starting rather than trusting the extension.

Two open source parts do the heavy lifting, and both are served from this site. Containers are parsed and audio is decoded by Mediabunny 1.55.7 under the MPL-2.0 (licence text, the exact package, source). MP3 encoding is lamejs 1.2.7 under the LGPL-3.0 (licence text, the exact package, corresponding source). Both are bundled unmodified at those versions and loaded from this page, never from another service.

Common questions

Can this convert a video without uploading it?: Yes. The MP4 is read and decoded in your browser, and only its audio track is encoded. No file bytes leave this device.
What if the MP4 has multiple audio tracks?: The page lists the available tracks with their codecs and channels so you can choose one before converting.

Files are decoded and re-encoded in your browser, so nothing is uploaded. Converting cannot restore detail a lossy file already lost: MP3 to WAV makes a larger file, not a better one. Which formats can be decoded depends on your browser, and this page checks the file's actual bytes and its codec before starting rather than trusting the extension.