Convert AU to M4A
Free online AU to M4A converter. No signup required.
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Max file size: 100 MB
When to convert AU to M4A
Use this conversion when your destination needs M4A and you have a AU source. Keep the original so you can compare the result or try another supported format.
Audio is decoded and re-encoded using format-specific defaults. Sample format and some metadata may change. Embedded cover art is omitted. A lossless destination cannot recover detail lost in the source.
AU vs M4A: Format Comparison
Side-by-side comparison of the source and target formats.
| Property | AU (Source) | M4A (Target) |
|---|---|---|
| Extension | .au | .m4a |
| Full Name | Sun AU Audio | M4A Audio |
| Compression | Varies | Lossy |
| File Size | Varies | Varies |
| Best For | Unix and Solaris system audio and sound effects | iTunes and Apple Music audio library storage |
| Browser Support | Varies | Limited |
How to Convert AU to M4A
Follow these simple steps to convert your file in seconds.
Choose a AU file
Select or drop one file up to 100 MB. Its extension must match this converter. Availability is checked before transfer.
Convert to M4A
Audio is decoded and re-encoded using format-specific defaults. Sample format and some metadata may change. Embedded cover art is omitted. A lossless destination cannot recover detail lost in the source.
Download and check the result
Use Download after conversion completes. Open the result and check its content, quality and formatting before sharing it. Download links expire one hour after upload finishes. Uploaded and converted files are removed automatically by regular cleanup. Files may become unavailable sooner when the service restarts.
Tips for Converting AU to M4A
Practical advice to get the best results from this conversion.
Why this conversion is worth doing
Sun AU Audio has a known limitation: largely obsolete for general-purpose audio use. M4A Audio addresses this with a key advantage: better audio quality than MP3 when using AAC encoding. Converting from AU to M4A is most worthwhile when this specific trade-off matters for the way you intend to use the file.
Match the format to the actual workflow
Sun AU Audio is most commonly used for unix and solaris system audio and sound effects, while M4A Audio is the standard for itunes and apple music audio library storage. If your workflow is closer to the second pattern, converting makes sense. If you are still working in a context where AU is the norm, converting may create unnecessary compatibility friction with collaborators or tools that expect the source format.
Watch for this limitation in the M4A output
M4A Audio has its own limitation worth understanding before you commit: slightly less universal compatibility than MP3 on older devices. After the conversion completes, open the M4A file and verify that this limitation does not affect your specific use case — for some workflows it is irrelevant; for others it can be a deal-breaker.
Understand lossy vs. lossless before converting
Converting from a lossy format like MP3 to a lossless format like FLAC or WAV does not restore lost audio data — it only changes the container. If you need true lossless quality, always start from an uncompressed or lossless source. Converting lossless to lossy, however, is a valid way to reduce file size for streaming or mobile playback.
Understanding AU and M4A Formats
Learn about the source and target file formats to understand what happens during conversion.
Source Format
Sun AU Audio
audio/basicAU is an audio file format introduced by Sun Microsystems and commonly associated with Unix and NeXT systems. It supports various encodings including uncompressed PCM, mu-law, and A-law compression, with a simple header structure. AU was one of the earliest audio formats supported on the web and remains used in Unix-based audio programming.
Advantages
- Simple, well-documented format with a minimal header
- Native support in Unix, Solaris, and Java audio APIs
- Supports multiple encoding types including mu-law for telephony
Limitations
- Largely obsolete for general-purpose audio use
- Limited metadata support and no modern compression options
- Poor support in consumer audio software and devices
Common Uses
- Unix and Solaris system audio and sound effects
- Java application audio playback (javax.sound)
- Legacy telephony and voice processing systems
Target Format
M4A Audio
audio/mp4M4A is an audio-only MPEG-4 container file that typically contains either AAC or Apple Lossless (ALAC) encoded audio. It was popularized by Apple as the default format for music purchased from the iTunes Store and ripped from CDs in iTunes. M4A files support rich metadata including album art, lyrics, and chapter markers.
Advantages
- Better audio quality than MP3 when using AAC encoding
- Supports both lossy (AAC) and lossless (ALAC) audio codecs
- Rich metadata support including album art, lyrics, and chapters
Limitations
- Slightly less universal compatibility than MP3 on older devices
- Can be confusing due to containing different codecs (AAC vs ALAC)
- Some older car stereos and portable players lack M4A support
Common Uses
- iTunes and Apple Music audio library storage
- Audiobooks and podcasts with chapter markers
- High-quality music distribution on Apple platforms
Frequently Asked Questions
Common questions about converting AU to M4A.
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