Add your AU file
Drop one or more .au 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.
AU to MP3
Re-encoding .au audio as .mp3 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 AU 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 Sun audio to MP3 audio
Re-encoding .au audio as .mp3 changes how the sound is compressed and which players will accept it. 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.
An .mp3 file stores audio compressed with MPEG Audio Layer III, the codec that made digital music portable. By discarding sounds the human ear masks anyway, .mp3 shrinks a CD track to roughly a tenth of its original size, a trade-off that reshaped the entire music industry. For this route the practical draw is plays on effectively every device made in the last twenty years and small files with respectable quality at 192 kbps and above — balanced against artifacts such as pre-echo on sharp transients become audible at low bitrates, which is worth knowing before you commit a large batch.
Why convert AU to MP3?
The practical trigger for this conversion is usually a mismatch: with .au, essentially obsolete outside legacy systems. Switching to .mp3 buys you plays on effectively every device made in the last twenty years, which is why it is the better fit for sharing music when the recipient's device is unknown. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
AU vs MP3 at a glance
| Aspect | Sun audio (.au) | MP3 audio (.mp3) |
|---|---|---|
| Format type | Lossless — every pixel or sample is preserved exactly | Lossy — discards detail it judges invisible to shrink files |
| How it stores data | a 24-byte header carries a '.snd' magic number, data offset, encoding type, sample rate, and channel count | lossy perceptual coding built on a hybrid filterbank and psychoacoustic masking model |
| Strongest at | maintaining sound assets in vintage Unix and Java software | sharing music when the recipient's device is unknown |
| Weak spot | essentially obsolete outside legacy systems | artifacts such as pre-echo on sharp transients become audible at low bitrates |
| Metadata | an optional annotation field in the header can hold a short text string; no formal tag structure exists | iD3v1 and ID3v2 tags carry title, artist, album, artwork, lyrics, and chapter frames; ID3v2.4 is the current revision |
Pick MP3 as the output
Select .mp3 in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if MP3 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 MP3 file. Outputs keep the original filename with the .mp3 extension.
AU to MP3 questions, answered
Will converting AU to MP3 lose quality?
Some. Since au is lossless-oriented and mp3 is lossy-oriented, the encoder will discard detail it judges least visible; the quality slider controls how aggressive that is. Keep the original .au if you may need a pristine master later.
Is it private to convert AU files here?
Yes — the .au 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 MP3 file work?
Every browser, operating system, phone, car stereo, and smart speaker of the modern era plays .mp3, making it the single safest audio format to hand to a stranger. Only antique hardware with narrow bitrate support ever struggles.
Will the MP3 file be bigger or smaller than my AU?
Smaller, usually dramatically so — that is the main reason this route exists. The quality slider trades size against fidelity; the default sits at the point where most people cannot spot the difference.
What happens to the metadata in my AU 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, an optional annotation field in the header can hold a short text string; no formal tag structure exists; none of it is transmitted anywhere because the file never leaves your browser.
Can I convert MP3 back to AU?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .au → .mp3 → .au is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.