Is it free to convert between AU and M4A?

Yes, Convert999 is 100% free. All conversions happen locally in your browser with no file size limits, no registration, and no watermarks.

.au

.m4a

AU vs M4A

Compare Sun Audio and MPEG-4 Audio formats — understand the key differences and when to use each

Format Overview

AU

Sun Audio

Sun Audio (.au) is a audio file format.

.auaudio

M4A

MPEG-4 Audio

MPEG-4 Audio (.m4a) is a audio file format.

.m4aaudio

AU vs M4A: Feature Comparison

Feature	AU	M4A
Full Name	Sun Audio	MPEG-4 Audio
File Extension	.au	.m4a
Category	audio	audio
Free to Convert	✓ Yes	✓ Yes
Browser Support	✓ All Browsers	✓ All Browsers
Convert to Each Other	✓ Yes	✓ Yes

When to Use AU vs M4A

Use AU when you need:

•Files in Sun Audio format for maximum compatibility
•Industry-standard audio format support
•Wide software and platform compatibility

Use M4A when you need:

•Files in MPEG-4 Audio format for specific workflows
•Optimized audio format features
•Modern format advantages and smaller file sizes

Convert Between Them

AU M4A M4A AU

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Frequently Asked Questions

What is the difference between AU and M4A?

AU (Sun Audio) and M4A (MPEG-4 Audio) are both audio file formats. AU files use the .au extension while M4A uses .m4a. They differ in compression, quality, compatibility, and intended use cases.

Can I convert AU to M4A for free?

Yes! Convert999 lets you convert AU to M4A completely free, directly in your browser. No file upload to any server, no registration needed — your files stay private on your device.

Which is better, AU or M4A?

It depends on your use case. AU (Sun Audio) may be better for certain workflows, while M4A (MPEG-4 Audio) excels in others. Consider factors like file size, quality, software compatibility, and your specific needs.

Is it safe to convert files on Convert999?

Absolutely. Convert999 processes all files 100% locally in your browser. Your files are never uploaded to any server, ensuring complete privacy and security.

AU Converter

Convert from AU

M4A Converter

Convert from M4A

File Tools

Compress, resize, merge

Convert to AU

All sources → AU

Convert to M4A

All sources → M4A

Format Statistics

Trends & data 2025

More Format Comparisons

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Feature

M4A

Full Name