Convert OPUS to AU

Tested on Windows 11, 24 October 2026

Convert OPUS audio to AU in your browser or in the Filoshi app for Windows. AU stores the decoded audio without further loss. Nothing is uploaded.

Get Filoshi · $29Many files at once, no size limit, on Windows.

How to convert OPUS to AU in your browser

  1. 1
    Drop your OPUS file
    Drag it onto Filoshi above, or press Choose your OPUS file to pick it on your computer.
  2. 2
    Filoshi converts it
    AU is chosen already. FFmpeg, compiled to WebAssembly, converts it inside this browser tab.
  3. 3
    Save your AU file
    Download it when it is ready. Nothing was sent to a server.
Source format

What is OPUS?

Opus Audio (.opus). Opus is an open, royalty-free codec standardised by the IETF in 2012. It sounds very good at low bitrates for both speech and music, and it is the codec of WebRTC video calls and many voice-message apps.

Common use: Voice messages, calls, streaming, podcasts

Output format

What is AU?

Sun Audio (.au). AU is Sun Microsystems' simple audio format from early Unix workstations: a short header followed by samples, often 8-bit µ-law or linear PCM. It appears in old Unix software and early web sound clips.

Common use: Old Unix sounds and early web audio

Questions about OPUS to AU

Is converting OPUS to AU free?
Yes, one file at a time: the converter on this page runs in your browser, files up to 100 MB, no sign-up. The Filoshi desktop app ($29 once, for Windows) converts many files at once and has no size limit.
Does converting OPUS to AU lose quality?
No further loss: AU keeps exactly what is decoded from the OPUS file. It cannot bring back detail that OPUS's lossy compression already removed, and the AU file is usually larger.
Is my OPUS file uploaded anywhere?
No. The converter on this page runs in your browser with FFmpeg compiled to WebAssembly; your OPUS file is read and converted on your device and never sent to a server. The desktop app works the same way, offline.
Has OPUS to AU been tested?
Yes. OPUS to AU is one of the 1,841 conversions that passed Filoshi's automated test matrix on Windows 11.
Can I convert many OPUS files at once?
Yes, in the desktop app. Drop as many OPUS files as you like on the window, pick AU once for all of them, and each file shows its own progress. The new files appear next to the originals, which are never changed.

Related conversions

Other OPUS conversions

OPUS to MP3OPUS to AACOPUS to OGGOPUS to FLACOPUS to M4AOPUS to AIFFOPUS to AC3OPUS to CAF

Convert to AU

MP3 to AUWAV to AUAAC to AUOGG to AUFLAC to AUM4A to AUWMA to AUAIFF to AU

Need OPUS to AU for many files?

The browser converter handles one file at a time. The Filoshi app for Windows converts as many as you drop, runs offline, and has 1,841 tested conversions.

Get Filoshi · $29