MP4 to AU Converter
Processing entirely on your device — large files may take a moment.
Converting AU to WAV preserves the samples in a format every modern tool reads. If your files are still in MP4 format, this page is the shortcut: MP4 (H.264) is the universal video format: every phone records it, every browser, TV, editor and chat app plays it.
This converter runs entirely in your browser using WebAssembly — your files never leave your device, nothing is uploaded, and there are no watermarks, sign-ups or queues. Drop in several files at once to convert them as a batch.
How MP4 compares to AU
| MP4 | AU | |
|---|---|---|
| Compression | H.264 / HEVC / AV1 + AAC | µ-law or PCM |
| Quality | Depends on encode settings | Mono voice-grade (µ-law) |
| Compatibility | Plays everywhere | Legacy Unix tools |
| Best for | Distribution, web, storage | Old system sounds and recordings |
How to convert MP4 to AU
- 1
Select your files
Select your MP4 video.
- 2
Convert instantly
The engine demuxes the container and encodes the audio track into your chosen format.
- 3
Download results
Download the AU audio — the video track is simply dropped.
About the MP4 format
MP4 (MPEG-4 Part 14) is the universal delivery container of digital video. It wraps H.264, HEVC or AV1 video with AAC audio, and its structure — separate metadata (moov) and media atoms — is what makes streaming, seeking and fast-start playback possible. Phones, cameras, TVs, browsers and every social platform assume MP4 first.
Quality is entirely a function of the codec and bitrate chosen at encode time, so an MP4 can be a 10 Mbps HEVC master or a postage stamp. That flexibility plus total playback coverage is why nothing has displaced it in twenty years — conversion between formats almost always ends in MP4.
+ Strengths
- ✓Plays on every device and platform in existence
- ✓Streaming-ready structure (fast start, seeking)
- ✓Choice of modern codecs: H.264, HEVC, AV1
! Limitations
- −Quality depends entirely on encode settings
- −HEVC variants hit licensing gaps on some platforms
About the AU format
AU is Sun Microsystems' audio format from the Unix workstation age: a small header followed by µ-law (or PCM) samples. Java's applet era shipped it everywhere, and old Unix sound tooling still emits it.
Modern players increasingly skip it. Converting AU to WAV preserves the samples bit-for-bit while moving the file into universal territory — the standard rescue path for system sounds and old recordings.
+ Strengths
- ✓Simple, lossless sample storage
- ✓Native to old Unix/Java tooling
! Limitations
- −µ-law flavor sounds dated and mono
- −Dropped by modern players
Why convert MP4 to AU?
There is a concrete reason this conversion exists: Quality depends entirely on encode settings AU sidesteps that — Simple, lossless sample storage If that is your situation, the tool above settles it in seconds, entirely on your device.
Frequently asked questions
Is this MP4 to AU converter really free?
Yes — completely free, with no sign-up, no watermark and no daily conversion limits. The site is supported by advertising.
Are my files uploaded to a server?
No. The conversion runs entirely inside your browser using WebAssembly, so your files never leave your device — that is what makes it instant and private.
Does it work on Windows, Mac, iPhone and Android?
Yes. Anything with a modern browser works: Windows, macOS, Linux, Android and iOS. No software installation is required.
Is there a file size limit for MP4 to AU?
The only limit is your device's memory, since nothing is uploaded. Files up to a few hundred megabytes work fine on a modern desktop browser; very large files simply take a little longer.
Why is video conversion slower than image conversion?
Every frame has to be decoded and re-encoded. This site runs that work on your own CPU via WebAssembly — nothing is uploaded, but a multi-minute video reasonably takes a few minutes. Images, by comparison, are single-frame jobs.
Will the audio track be kept?
Yes. The audio is carried over and re-encoded to the standard audio codec of AU, staying in sync with the video. If your MP4 file has multiple audio tracks, the first one is used.