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 AC3
Re-encoding .au audio as .ac3 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 Dolby Digital audio
Re-encoding .au audio as .ac3 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 .ac3 file holds a raw Dolby Digital bitstream, the surround-sound format of DVDs, digital television, and countless movie soundtracks. Files with the .ac3 extension usually appear after audio has been demuxed from a disc or video file for editing or conversion. For this route the practical draw is universally decoded by home-theater receivers, soundbars, and TVs and keeps 5.1 mixes exactly as the studio authored them — balanced against browsers mostly lack the decoder, so MP4s with AC-3 audio often play silent video on the web, which is worth knowing before you commit a large batch.
Why convert AU to AC3?
The practical trigger for this conversion is usually a mismatch: with .au, essentially obsolete outside legacy systems. Switching to .ac3 buys you universally decoded by home-theater receivers, soundbars, and TVs, which is why it is the better fit for preserving the original surround track when remuxing DVDs into MKV. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
AU vs AC3 at a glance
| Aspect | Sun audio (.au) | Dolby Digital audio (.ac3) |
|---|---|---|
| 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 | a perceptual MDCT transform codec carrying up to 5.1 channels |
| Strongest at | maintaining sound assets in vintage Unix and Java software | preserving the original surround track when remuxing DVDs into MKV |
| Weak spot | essentially obsolete outside legacy systems | browsers mostly lack the decoder, so MP4s with AC-3 audio often play silent video on the web |
| Metadata | an optional annotation field in the header can hold a short text string; no formal tag structure exists | no tagging layer exists; the bitstream carries technical metadata like dialnorm and downmix coefficients rather than titles or artists |
Pick AC3 as the output
Select .ac3 in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if AC3 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 AC3 file. Outputs keep the original filename with the .ac3 extension.
AU to AC3 questions, answered
Will converting AU to AC3 lose quality?
Some. Since au is lossless-oriented and ac3 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 AC3 file work?
Home-theater equipment decodes Dolby Digital as a matter of course, and Windows and macOS handle it in their native players, but browser support is nearly nonexistent. Transcoding the track to AAC is the standard remedy when web playback matters.
Will the AC3 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 AC3 back to AU?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .au → .ac3 → .au is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.