AU to M4A Converter
Processing entirely on your device — large files may take a moment.
Sun Microsystems Audio and MPEG-4 Audio exist for different jobs: AU is the µ-law audio format of old Unix systems and Java applets — tiny mono files from another era. M4A sounds better than MP3 at the same bitrate, and Apple users never have compatibility worries.
Because the whole conversion happens on your device, it is instant, unlimited and genuinely private — no accounts, no watermarks, no files on anyone's server. Multiple files are converted in one go.
How AU compares to M4A
| AU | M4A | |
|---|---|---|
| Compression | µ-law or PCM | Lossy AAC (ALAC for lossless) |
| Quality | Mono voice-grade (µ-law) | Strong at 128–256 kbps |
| Compatibility | Legacy Unix tools | Apple-first, modern platforms |
| Best for | Old system sounds and recordings | Music libraries and voice memos |
How to convert AU to M4A
- 1
Select your files
Drag & drop your AU files onto the area above, or click to browse. You can add multiple files at once for batch conversion.
- 2
Convert instantly
Click "Convert to M4A". The conversion runs entirely inside your browser using WebAssembly — no upload, no queue, no waiting.
- 3
Download results
Download each converted M4A file individually, or grab everything at once as a ZIP archive.
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
About the M4A format
M4A is MPEG-4 audio: AAC (or ALAC) inside the MP4 container, minus the video. It became the iTunes Store's format in 2003 and never left — Apple Music downloads, voice memos and most phone recordings are M4A. At the same bitrate, AAC sounds distinctly better than MP3, which is why 128 kbps M4A competes with 192 kbps MP3.
Support is excellent across Apple devices, modern Android, Windows and every streaming SDK. The one historical caveat: iTunes Store music bought before 2009 carried FairPlay DRM; everything since (and everything you record yourself) is DRM-free.
+ Strengths
- ✓Better quality than MP3 at the same bitrate
- ✓First-class on Apple and modern platforms
- ✓ALAC variant covers lossless needs
! Limitations
- −Very old feature phones and players miss it
- −Pre-2009 store purchases may carry DRM
Why convert AU to M4A?
Think of it as moving your file to the container that fits the job. µ-law flavor sounds dated and mono M4A works differently: Better quality than MP3 at the same bitrate If any of that sounds like your task, run the conversion — it takes seconds and nothing leaves your device.
Frequently asked questions
Is this AU to M4A 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 AU to M4A?
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.
Can I convert a whole folder of AU files?
You can select many files at once and they are processed in a single batch. Output files land in one ZIP download when there is more than one result.
Will converting AU to M4A reduce audio quality?
If M4A is lossless, the output contains everything the AU file contains — no further loss is added. If M4A is lossy, one recompression pass is unavoidable; the quality slider controls how much. Loss that already happened in the source file can never be undone by converting.