What is a .au file?
Sun Audio · Audio · Sun Microsystems / NeXT · 1992
An .au file is Sun audio, one of the oldest digital sound formats, from Unix workstations and early Java. It starts with the marker .snd and usually holds simple uncompressed or mu-law encoded sound.
What is a .au file used for?
AU files begin with the four bytes .snd and a short header giving the encoding and sample rate. They were the standard sound format on Sun and NeXT systems and in early Java applets.
The format is legacy now. VLC and Audacity open it; convert to WAV or MP3 for modern use.
What opens a .au file?
The .au format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- VLC
- Audacity
- foobar2000
macOS
- VLC
- Audacity
- QuickTime
Linux
- VLC
- Audacity
- ffmpeg
Open a .au file step by step
- Confirm the file really is a .au. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with VLC or Audacity.
- On Mac, use VLC or Audacity.
- On Linux, try VLC or Audacity.
- Still stuck? Convert the .au to wav, which opens more widely.
Why can't I open my .au file?
Almost always because no installed app understands AU. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .au at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .au file
You can convert a .au file to wav, mp3, flac using a conversion tool or the export menu of an app that opens it.
What is the .au file signature (magic bytes)?
A .au file starts with the hex bytes 2E 73 6E 64, which read as .snd in ASCII. Programs identify AU by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for AU. For a full breakdown, see the Sun audio (.snd) file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 2E 73 6E 64 | 0 | .snd | '.snd' |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .au file?
An .au file is Sun audio, one of the oldest digital sound formats, from Unix workstations and early Java. It starts with the marker .snd and usually holds simple uncompressed or mu-law encoded sound.
How do I open an .au file?
Play it in VLC or open it in Audacity. To use it elsewhere, convert it to WAV or MP3.
What is a .au file?
Sun audio, an old Unix and Java sound format that starts with the .snd marker. It is largely historical today.
Is .au the same as .snd?
Effectively yes. The format's magic bytes are .snd, and some systems used the .snd extension for the same Sun audio format.
Related formats
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