Convert AU to M4A
Free online AU to M4A converter. No signup required.
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Max file size: 100 MB
Why Convert AU to M4A?
Understand when and why this conversion makes sense for your workflow.
Converting Sun AU Audio to M4A Audio ensures your audio files work across the widest possible range of devices, players, and streaming platforms. Audio formats differ significantly in their compression algorithms, bitrate support, and metadata handling. Whether you're archiving a music collection, preparing tracks for a podcast, or optimizing audio for a mobile app, selecting the right output format is essential for balancing playback compatibility with sound fidelity.
Sun AU Audio has a known limitation: largely obsolete for general-purpose audio use. In contrast, M4A Audio offers a key advantage: better audio quality than MP3 when using AAC encoding. While Sun AU Audio is commonly used for unix and solaris system audio and sound effects, M4A Audio is better suited for itunes and apple music audio library storage.
MegaConvert processes your AU file and delivers a properly encoded M4A output, preserving audio quality within the limits of the target format — free, instant, and private.
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.
Upload your AU audio
Drop your .au audio file into the upload zone or browse to select it. Both short voice clips and full-length tracks work — typical Sun AU Audio files (under 100 MB) upload in seconds even on a slow connection. Album art and metadata in the file are read automatically.
Start the M4A encode
Press the convert button to start. The audio stream is decoded from Sun AU Audio into PCM, then re-encoded as M4A Audio at a quality preset that matches the source bitrate where possible. Sample rate, channel count, and bit depth are preserved unless the target format restricts them.
Wait for the audio to finish encoding
Encoding speed depends on the length of the audio and the codec. Short clips finish in a few seconds; full-length albums can take 30 seconds or so. We do not throttle conversions — the limit is just the encoder's natural speed on the underlying hardware.
Download your .m4a file
When the conversion finishes, click the download link to save the new M4A Audio file to your computer. The file is yours — no watermarks, no expiration on the file itself, and no MegaConvert account is required to download it.
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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