AU to OPUS Converter
Processing entirely on your device — large files may take a moment.
Sun Microsystems Audio and Opus Audio exist for different jobs: AU is the µ-law audio format of old Unix systems and Java applets — tiny mono files from another era. Opus delivers the smallest files with the best quality for streaming and messaging.
Because the whole conversion happens on your device, it is instant, unlimited and genuinely private — no accounts, no watermarks, no files on anyone's server. Multiple files are converted in one go.
How AU compares to OPUS
| AU | OPUS | |
|---|---|---|
| Compression | µ-law or PCM | Lossy (6–510 kbps) |
| Quality | Mono voice-grade (µ-law) | State of the art |
| Compatibility | Legacy Unix tools | Software strong, hardware lagging |
| Best for | Old system sounds and recordings | Calls, live streams, chat |
How to convert AU to OPUS
- 1
Select your files
Drag & drop your AU files onto the area above, or click to browse. You can add multiple files at once for batch conversion.
- 2
Convert instantly
Click "Convert to OPUS". The conversion runs entirely inside your browser using WebAssembly — no upload, no queue, no waiting.
- 3
Download results
Download each converted OPUS file individually, or grab everything at once as a ZIP archive.
About the AU format
AU is Sun Microsystems' audio format from the Unix workstation age: a small header followed by µ-law (or PCM) samples. Java's applet era shipped it everywhere, and old Unix sound tooling still emits it.
Modern players increasingly skip it. Converting AU to WAV preserves the samples bit-for-bit while moving the file into universal territory — the standard rescue path for system sounds and old recordings.
+ Strengths
- ✓Simple, lossless sample storage
- ✓Native to old Unix/Java tooling
! Limitations
- −µ-law flavor sounds dated and mono
- −Dropped by modern players
About the OPUS format
Opus (IETF RFC 6716, 2012) is the codec that ended the argument: it merges Skype's CELT and Xiph's SILK into one royalty-free format that is simultaneously the best low-latency speech codec and a superb music codec. WebRTC calls, Discord, WhatsApp, WhatsApp calls, YouTube's low-bitrate streams and Zoom all run on it.
At 6 kbps it keeps speech intelligible; at 128 kbps it is transparent for music; latency can dip below 5 ms for live conversation. Its weakness is hardware: dedicated chips and some car/hi-fi devices still lack it, and standalone .opus files are less recognized than MP3 on random devices.
+ Strengths
- ✓Best quality-per-bit across speech and music
- ✓Ultra-low latency — built for live calls
- ✓Royalty-free IETF standard
! Limitations
- −Hardware support still incomplete
- −Not a mastering or archival format
Why convert AU to OPUS?
Converting makes sense where the strengths of OPUS meet what AU cannot give you. Best quality-per-bit across speech and music Meanwhile µ-law flavor sounds dated and mono One pass through the converter above puts your file on the right side of that trade-off.
Frequently asked questions
Is this AU to OPUS converter really free?
Yes — completely free, with no sign-up, no watermark and no daily conversion limits. The site is supported by advertising.
Are my files uploaded to a server?
No. The conversion runs entirely inside your browser using WebAssembly, so your files never leave your device — that is what makes it instant and private.
Does it work on Windows, Mac, iPhone and Android?
Yes. Anything with a modern browser works: Windows, macOS, Linux, Android and iOS. No software installation is required.
Is there a file size limit for AU to OPUS?
The only limit is your device's memory, since nothing is uploaded. Files up to a few hundred megabytes work fine on a modern desktop browser; very large files simply take a little longer.
Will converting AU to OPUS reduce audio quality?
If OPUS is lossless, the output contains everything the AU file contains — no further loss is added. If OPUS is lossy, one recompression pass is unavoidable; the quality slider controls how much. Loss that already happened in the source file can never be undone by converting.
Are tags like title and artist preserved?
Tag handling varies between target formats and this conversion focuses on the audio itself. For archival copies where tags matter, keep the original file; the converted copy is for playback and sharing.