M4A Won't Open? Convert to AU Instantly
Fast, instant M4A to AU conversion. No signup required. Just drop your .m4a file and get .au in seconds.
Batch Settings
Vous manipulez des fichiers audio et avez besoin de convertir vos M4A en AU ? Que ce soit pour des raisons de compatibilité logicielle, d'archivage ou d'intégration dans des systèmes spécifiques, cette conversion est souvent indispensable. Le format M4A, couramment associé aux contenus Apple, offre une excellente qualité avec une bonne compression. Cependant, le format AU, bien que moins répandu aujourd'hui, reste un standard robuste, particulièrement dans les environnements Unix et pour certaines applications professionnelles ou scientifiques où sa simplicité structurelle est appréciée. Notre outil vous permet d'effectuer cette transformation avec aisance, garantissant l'intégrité de votre signal audio. Simplifiez votre flux de travail et assurez la compatibilité de vos projets en quelques clics, sans compromettre la fidélité sonore.
- Archivage de données sonores pour les administrations publiques (France)
- Intégration dans des plateformes éducatives universitaires (Québec)
- Échanges de fichiers entre studios de design sonore (Belgique)
Dans les milieux académiques et de recherche francophones, notamment en Suisse, le format AU peut encore être rencontré pour des corpus sonores anciens ou des systèmes d'analyse spécifiques, où la simplicité de son en-tête est parfois préférée. La conversion M4A vers AU y est donc un besoin réel.
About M4A to AU Conversion
Dealing with a M4A file that won't open on your device? You're not alone — M4A compatibility issues are one of the most common reasons people search for a file converter. M4A is an AAC audio file in an MPEG-4 container — common for Apple Music and iTunes downloads.
The fix is simple: convert your M4A to AU. AU is a widely used file format. This conversion lets you convert between formats quickly, solving the problem in seconds rather than hours of troubleshooting.
Converting M4A to AU maintains high quality with CocoConvert's optimised encoder settings.
CocoConvert processes your M4A file on secure servers in Germany — upload, convert, download. Your files are encrypted via TLS and automatically deleted within 24 hours. No account needed, no software to install, and it works on any device with a browser.
This conversion is ideal when you When you need a AU file.
The conversion engine behind CocoConvert uses FFmpeg, Sharp, and qpdf — the same open-source libraries trusted by Netflix, YouTube, and enterprise platforms. Pro users can batch convert up to 100 files at once.
How to Convert M4A to AU
- 1
Add your M4A file
Drag and drop your .m4a file into the converter, or tap "Browse" to pick it from your device. Multiple files are supported for batch processing.
- 2
Pick AU output
Select .au as the target format. CocoConvert automatically applies the best quality settings for this conversion.
- 3
Start conversion
Hit the Convert button. The audio engine processes your file server-side — no CPU drain on your device.
- 4
Save your file
Once done, download your .au file. For batch jobs, download all at once as a zip.
What Happens When You Convert M4A to AU
Your M4A file is decoded and re-encoded as AU.
Your M4A file is uploaded and validated
The file is decoded (parsed into its raw data)
The data is re-encoded in AU format
The converted file is ready for download
Format Comparison
M4A
.m4a file
| Extension | .m4a |
| MIME Type | audio/mp4 |
| Category | Audio |
AU
.au file
| Extension | .au |
| MIME Type | audio/basic |
| Category | Audio |
Should You Convert M4A to AU?
When to Convert
- ✓When you need a AU file
Frequently Asked Questions
Why won't my M4A file open?
M4A files may not open if your device lacks the right codec or application. Converting to AU — a more widely supported format — usually resolves this. AU is a widely used file format.
Is it safe to convert M4A to AU online?
Yes. CocoConvert encrypts your file via TLS, processes it on isolated servers in Germany, and permanently deletes it within 24 hours. Your files are never shared or analysed.
Will I lose quality converting M4A to AU?
Converting M4A to AU maintains high quality with CocoConvert's optimised encoder settings. CocoConvert uses high-quality encoder defaults to preserve as much fidelity as possible.
How large can my M4A file be?
Free users can convert files up to 250 MB each. Pro users get a 5 GB limit per file, and Business API users have custom limits.
Can I convert M4A to AU on my phone?
Absolutely. CocoConvert works in any modern browser — iOS Safari, Android Chrome, and all desktop browsers. No app required.
Versions are pinned in our worker Dockerfile and re-built via CI on every change.