Add your OPUS file
Drop one or more .opus files onto the converter above, or browse for them. They load into browser memory only — nothing is uploaded, so there is no size-based pricing and no server queue.
OPUS to AU
Re-encoding .opus audio as .au changes how the sound is compressed and which players will accept it. Free, private, and validated — the file never leaves your browser.
Private for supported formats — processed in your browser
Runs on your deviceConvert supported files
Drop OPUS files here
Batch files can each use a different output. Nothing uploads for local conversions.
Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.About converting Opus audio to Sun audio
Re-encoding .opus audio as .au changes how the sound is compressed and which players will accept it. An .opus file contains audio compressed with the Opus codec, stored in an Ogg container. Opus represents the current state of the art in lossy audio, beating MP3, AAC, and Vorbis in listening tests at nearly every bitrate from whisper-thin speech settings up to transparent music encoding.
An .au file is the Sun audio format, one of the earliest structured audio files, created for Unix workstations. A minimal header followed by sample data, classically 8 kHz mu-law telephony audio, makes .au about as simple as an audio format can get. For this route the practical draw is so simple that nearly any audio tool can parse it and pCM variants preserve the recording exactly — balanced against essentially obsolete outside legacy systems, which is worth knowing before you commit a large batch.
Why convert OPUS to AU?
The practical trigger for this conversion is usually a mismatch: with .opus, older car stereos, AV receivers, and MP3 players have never heard of it. Switching to .au buys you so simple that nearly any audio tool can parse it, which is why it is the better fit for maintaining sound assets in vintage Unix and Java software. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
OPUS vs AU at a glance
| Aspect | Opus audio (.opus) | Sun audio (.au) |
|---|---|---|
| Format type | Lossy — discards detail it judges invisible to shrink files | Lossless — every pixel or sample is preserved exactly |
| How it stores data | the hybrid SILK/CELT design switches coding modes automatically based on content | a 24-byte header carries a '.snd' magic number, data offset, encoding type, sample rate, and channel count |
| Strongest at | compressing podcast and voice-chat audio to tiny files | maintaining sound assets in vintage Unix and Java software |
| Weak spot | older car stereos, AV receivers, and MP3 players have never heard of it | essentially obsolete outside legacy systems |
| Metadata | vorbis comments in the OpusTags header, including cover art via METADATA_BLOCK_PICTURE, plus an output-gain field used for loudness normalization | an optional annotation field in the header can hold a short text string; no formal tag structure exists |
Pick AU as the output
Select .au in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if AU is selectable, the route is real and validated.
Convert on your device
Press Convert. The transcode runs on an FFmpeg engine compiled to WebAssembly, so the audio never leaves your device.
Verify and download
Each result is signature-checked before the download unlocks, so a failed encode can never masquerade as a valid AU file. Outputs keep the original filename with the .au extension.
OPUS to AU questions, answered
Will converting OPUS to AU lose quality?
No new loss is introduced — since opus is lossy-oriented and au is lossless-oriented, everything the .opus file still contains is carried over exactly. What was already discarded by the original lossy encode cannot be recovered, though; converting to .au does not "restore" quality.
Is it private to convert OPUS files here?
Yes — the .opus file is processed inside your browser tab and never uploaded. The transcode runs on an FFmpeg engine compiled to WebAssembly, so the audio never leaves your device. Close the tab and the file is gone from memory.
Where will the AU file work?
Audio tools such as Audacity, sox, and ffmpeg open .au readily, and Java's sound APIs still accept it. Consumer players, phones, and browsers dropped meaningful support long ago, so conversion to WAV or MP3 is the practical route.
Will the AU file be bigger or smaller than my OPUS?
Larger, sometimes much larger. A lossless .au must store every pixel or sample the decoder produced, without the perceptual shortcuts .opus used. Use this route for editing headroom, not for saving space.
What happens to the metadata in my OPUS file?
This converter strips container metadata deliberately (the FFmpeg command runs with metadata mapping disabled) so exported files do not leak recording details. In the source, vorbis comments in the OpusTags header, including cover art via METADATA_BLOCK_PICTURE, plus an output-gain field used for loudness normalization; none of it is transmitted anywhere because the file never leaves your browser.
Can I convert AU back to OPUS?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .opus → .au → .opus is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.