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
您是否曾遇到这样的情况：手头有一些M4A格式的音频文件，但在某些特定设备或老旧系统上却无法顺利播放？尤其是在处理一些早期录音、游戏音效或是需要跨平台兼容的场景时，M4A的普及性虽然高，但其兼容性有时却不如AU格式。AU，作为一种相对开放且历史悠久的音频格式，在许多专业音频编辑软件和UNIX类系统中拥有良好的原生支持。将M4A转换为AU，不仅能解决兼容性问题，还能为您的音频内容带来更广泛的应用可能。无论是为了在特定应用中流畅使用，还是为了保证音频在不同操作系统间的无缝传输，这次转换都能为您提供一个可靠的解决方案，让您的音频资产焕发新的活力。
- 旧款游戏机音效编辑
- 专业音频工作站兼容
- UNIX/Linux系统音频处理
在华语区，特别是处理一些早期游戏或教育软件的音频资源时，AU格式有时仍是某些特定开发环境或老旧系统默认或偏好的选择，转换能确保更好的兼容性和减少播放障碍。
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.