What quality should I expect from the AU output?

Our converter preserves as much fidelity as Sun AU Audio allows. Where M4A Audio carries information that Sun AU Audio cannot represent, that information is mapped to the closest equivalent (for example, color spaces, codec parameters, or metadata fields). For most everyday uses the result is indistinguishable from the source.

Will my audio metadata (title, artist, album, cover art) be preserved?

Yes, where the target format supports it. Sun AU Audio can carry standard tag information (ID3, Vorbis comments, or the equivalent depending on the format), and we copy as much metadata as possible from your M4A file. Cover art and embedded album artwork are preserved when both formats support it. Highly format-specific metadata that has no equivalent in AU is dropped.

What file size should I expect for the AU output?

The output size depends on the content and the compression characteristics of Sun AU Audio. In most cases the AU file will be in the same ballpark as your M4A input, with differences driven by how each format encodes data. There is no fixed ratio — the converter does not change quality settings unless you ask it to.

When should I convert M4A to AU instead of staying with M4A?

Convert when the application, device, or workflow you are targeting prefers Sun AU Audio over M4A Audio. If your current M4A file already opens and behaves correctly everywhere you need it to, there is no benefit to converting — keep the original. The most common reasons to switch are compatibility (a tool only accepts AU), distribution (recipients expect AU), or feature requirements specific to Sun AU Audio.

What is the maximum M4A file size I can convert?

MegaConvert accepts M4A files up to 100 MB on the free service, which is enough for the vast majority of real-world M4A Audio files. If you have a larger file (typical for high-resolution video or uncompressed audio), please contact us — we can sometimes accommodate larger uploads for legitimate use cases.

Is my M4A file safe and private when I upload it?

Yes. Your M4A file is uploaded over HTTPS, processed in an isolated job environment, and deleted from our servers within one hour. We do not read, index, store, or share the contents of your file. No account is required, so the upload is not associated with a personal identity. See our privacy policy for the full details.

Convert M4A to AU

Free online M4A to AU converter. No signup required.

Drag & drop your file here

or click to browse

Max file size: 100 MB

Why Convert M4A to AU?

Understand when and why this conversion makes sense for your workflow.

Converting M4A Audio to Sun AU 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.

M4A Audio has a known limitation: slightly less universal compatibility than MP3 on older devices. In contrast, Sun AU Audio offers a key advantage: simple, well-documented format with a minimal header. While M4A Audio is commonly used for itunes and apple music audio library storage, Sun AU Audio is better suited for unix and solaris system audio and sound effects.

MegaConvert processes your M4A file and delivers a properly encoded AU output, preserving audio quality within the limits of the target format — free, instant, and private.

M4A vs AU: Format Comparison

Side-by-side comparison of the source and target formats.

Property	M4A (Source)	AU (Target)
Extension	.m4a	.au
Full Name	M4A Audio	Sun AU Audio
Compression	Lossy	Varies
File Size	Varies	Varies
Best For	iTunes and Apple Music audio library storage	Unix and Solaris system audio and sound effects
Browser Support	Limited	Varies

How to Convert M4A to AU

Follow these simple steps to convert your file in seconds.

Upload your M4A audio
Drop your .m4a audio file into the upload zone or browse to select it. Both short voice clips and full-length tracks work — typical M4A 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 AU encode
Press the convert button to start. The audio stream is decoded from M4A Audio into PCM, then re-encoded as Sun AU 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 .au file
When the conversion finishes, click the download link to save the new Sun AU 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 M4A to AU

Practical advice to get the best results from this conversion.

Why this conversion is worth doing

M4A Audio has a known limitation: slightly less universal compatibility than MP3 on older devices. Sun AU Audio addresses this with a key advantage: simple, well-documented format with a minimal header. Converting from M4A to AU 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

M4A Audio is most commonly used for itunes and apple music audio library storage, while Sun AU Audio is the standard for unix and solaris system audio and sound effects. If your workflow is closer to the second pattern, converting makes sense. If you are still working in a context where M4A is the norm, converting may create unnecessary compatibility friction with collaborators or tools that expect the source format.

Watch for this limitation in the AU output

Sun AU Audio has its own limitation worth understanding before you commit: largely obsolete for general-purpose audio use. After the conversion completes, open the AU 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 M4A and AU Formats

Learn about the source and target file formats to understand what happens during conversion.

Source Format

M4A Audio

audio/mp4

M4A 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

Target Format

Sun AU Audio

audio/basic

AU 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

Frequently Asked Questions

Common questions about converting M4A to AU.

Related Conversions

Explore other conversions related to M4A and AU.

Other conversions from M4A

M4A to MP3 M4A to WAV M4A to FLAC M4A to AAC M4A to OGG M4A to WMA M4A to OPUS M4A to AIFF M4A to AMR M4A to AC3

Other conversions to AU

MP3 to AU WAV to AU FLAC to AU AAC to AU OGG to AU WMA to AU OPUS to AU AIFF to AU AMR to AU AC3 to AU

Convert M4A to AU

Why Convert M4A to AU?

M4A vs AU: Format Comparison

How to Convert M4A to AU

Upload your M4A audio

Start the AU encode

Wait for the audio to finish encoding

Download your .au file

Tips for Converting M4A to AU

Why this conversion is worth doing

Match the format to the actual workflow

Watch for this limitation in the AU output

Understand lossy vs. lossless before converting

Understanding M4A and AU Formats

M4A Audio

Advantages

Limitations

Common Uses

Sun AU Audio

Advantages

Limitations

Common Uses

Frequently Asked Questions

What quality should I expect from the AU output?

Will my audio metadata (title, artist, album, cover art) be preserved?

What file size should I expect for the AU output?

When should I convert M4A to AU instead of staying with M4A?

What is the maximum M4A file size I can convert?

Is my M4A file safe and private when I upload it?

Related Conversions

Other conversions from M4A

Other conversions to AU