About · updated 23 October 2026
mp4tomp3.net is a single-purpose audio tool.
The whole product is this page: converter for MP4 to MP3. It runs in the browser, without an account, an upload or a queue.
mp4tomp3.net converts MP4 video to MP3 audio in the browser; the file is never uploaded.
Why this site exists
Most “free online converters” upload the file to a server, process it there, and keep it for a while. That is a reasonable business, but it is not necessary for a format change this small. Modern browsers can read the container, decode the audio and encode the output locally. This site exists to do exactly that and to state the limits honestly.
How it is built
mp4tomp3.net uses Mediabunny for container reading, audio decoding and muxing. MP3 output uses a WASM build of the LAME encoder inside a worker. The page is a static Astro site with no application server, no database and no upload endpoint. The only third-party request is the aggregate analytics script.
How it is tested
The engine is checked against fixed fixtures on every change: MP4/AAC, MOV/AAC, MOV/ProRes with PCM, M4A/AAC, M4A/ALAC (must fail), WAV 16-bit, WAV 24-bit/96 kHz, MP3, a silent MP4, a truncated MP4, a 5.1 source, a MOV with two audio tracks, and a trimmed file. Outputs are verified with ffprobe for codec, duration, sample rate and channel count. Visual checks cover desktop and mobile widths, keyboard focus, overflow and colour contrast.
What it deliberately does not do
- It does not upload files for server-side processing.
- It does not fetch a URL or download from a streaming service.
- It does not remove DRM or convert protected purchases.
- It does not claim lossless MP3 output, unlimited file size, or a VBR control it cannot honour.
- It does not carry chapters, cover art or codecs the target format cannot store.
Who runs it
This site is maintained by an independent publisher that builds small, single-purpose browser tools. It is not affiliated with Apple, Microsoft, the LAME project or any streaming service. Corrections are applied as dated revisions on the page that changed.
Standards and terms
How facts are checked, what this site will not claim and how corrections work is set out in the editorial standards. The plain-language terms of use cover acceptable use, the no-warranty line and the limits of a browser-based converter.
Reporting a problem
A contact address is being set up. Until it is published, the how-it-works page documents the known limits and failure modes. Changes are dated at the top of each page.
Privacy in one paragraph
Files are never uploaded. The page counts visits with an aggregate analytics script and stores no cookies for the tool itself. Full detail is on the privacy page.