AU to M4A Converter
Convert AU to M4A online for free. Fast, secure, and high-quality conversion with no sign-up or software required.
Maximum file size is 1GB
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Three steps to your converted file
Everything happens in your browser tab - upload, pick a format, download. The heavy lifting runs on our servers.
Upload your file
Drag and drop, click to browse, or paste a URL. Batches take up to 20 files at once - 230+ input formats across video, audio, image, document, and archive types.
Choose an output format
Pick from over a hundred output formats. Filter by category or search by name - every option is open to everyone, no account needed.
Convert & download
Hit Convert and grab your download link moments later. Originals are erased when the job completes; results are cleared within about an hour.
What is an AU file?
The AU file format is a simple container format introduced by Sun Microsystems and NeXT for UNIX-based systems. It typically contains μ-law (mu-law) logarithmic encoded audio data (G.711 standard) stored in a big-endian byte order, identified by the hexadecimal magic number 0x2e736e64 ('.snd'). The file structure consists of a minimal 24-byte header specifying data offset, sample rate, and encoding type, followed by an optional annotation block and the contiguous audio data, making it a standard for early Web audio (Java applets) and SPARCstation workstations.
How to open an AU file
Modern operating systems often lack direct associations for AU files due to their obsolescence. While some Linux distributions and macOS (via Core Audio) may support basic playback, Windows requires third-party software. The VLC media player is the primary recommendation for opening AU files across all platforms; alternatively, Audacity can be used to import the raw data and convert it to modern PCM formats like WAV.
AU Technical Info
- Full Name
- Sun Microsystems Audio
- Developed By
- Sun Microsystems / NeXT
- Initial Release
- 1988
- MIME Type
- audio/basic
What is an M4A file?
The M4A file extension denotes an audio-only MPEG-4 container, defined by ISO/IEC 14496-14 standards and typically encoded using Advanced Audio Coding (AAC) or Apple Lossless (ALAC). Originally popularized by Apple to differentiate audio content from standard .MP4 video files, the container utilizes an atom-based structure (e.g., ftyp, moov, mdat) to store audio streams and metadata. It serves as the successor to MP3, offering superior compression efficiency and fidelity at equivalent bitrates.
How to open an M4A file
M4A files are natively supported by the Apple ecosystem (iTunes, QuickTime, iOS Music) and Windows Media Player on modern Windows versions. Cross-platform compatibility is robust, with VLC Media Player, Audacity, and Winamp providing decoding capabilities. On Android devices, native players often handle M4A, though third-party apps like Poweramp ensure compatibility with ALAC-encoded variants.
M4A Technical Info
- Full Name
- MPEG-4 Audio
- Developed By
- Apple Inc. / MPEG
- Initial Release
- 2001
- MIME Type
- audio/mp4
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The fastest way to convert any file
Purpose-built for speed, privacy, and breadth of format support.
Convert AU to M4A in seconds
Every AU to M4A conversion runs on our servers, so your device stays fast and the output quality stays intact.
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No queue, no waiting. Files are processed on high-performance servers and returned in seconds, even for large files.
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Encrypted in transit and never shared with anyone. Uploads are erased the moment your job completes, and results shortly after.
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Developer API
Convert AU to M4A via API
Automate AU to M4A conversions in three steps: create a job, upload your file, then poll for the result.
# 1. Create job
curl -X POST https://api.runconvert.com/v3/jobs \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"tag": "au-to-m4a",
"tasks": {
"upload-file": {
"operation": "import/upload"
},
"convert": {
"operation": "convert",
"input": "upload-file",
"output_format": "m4a"
},
"export-result": {
"operation": "export/url",
"input": "convert"
}
}
}'
# 2. Upload your file (use upload_url from the response)
curl -X PUT "$UPLOAD_URL" --upload-file input.au
# 3. Poll for result
curl https://api.runconvert.com/v3/jobs/$JOB_ID?include=tasks \
-H "Authorization: Bearer YOUR_API_KEY"Replace YOUR_API_KEY with your RunConvert API key. Get your free API key at runconvert.com/api.