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 M4R
Re-encoding .au audio as .m4r changes how the sound is compressed and which players will accept it. Free, private, and validated — the file never leaves your browser.
100% private for supported formats
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 Apple ringtone
Re-encoding .au audio as .m4r 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 .m4r file is an iPhone ringtone: AAC audio in an MPEG-4 container, identical to an .m4a in everything but the extension. Apple uses .m4r purely as a routing marker so iTunes and iOS file the audio under Tones instead of Music. For this route the practical draw is the only ringtone format iOS accepts and full AAC quality, indistinguishable from the source track — balanced against tones over 40 seconds are rejected outright, which is worth knowing before you commit a large batch.
Why convert AU to M4R?
The practical trigger for this conversion is usually a mismatch: with .au, essentially obsolete outside legacy systems. Switching to .m4r buys you the only ringtone format iOS accepts, which is why it is the better fit for turning a favorite song's hook into a custom iPhone ringtone. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
AU vs M4R at a glance
| Aspect | Sun audio (.au) | Apple ringtone (.m4r) |
|---|---|---|
| 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 | shares the ISO base media layout of .m4a, carrying AAC-LC audio |
| Strongest at | maintaining sound assets in vintage Unix and Java software | turning a favorite song's hook into a custom iPhone ringtone |
| Weak spot | essentially obsolete outside legacy systems | tones over 40 seconds are rejected outright |
| Metadata | an optional annotation field in the header can hold a short text string; no formal tag structure exists | standard iTunes atoms apply, though iOS shows only the title in the ringtone picker |
Pick M4R as the output
Select .m4r in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if M4R 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 M4R file. Outputs keep the original filename with the .m4r extension.
AU to M4R questions, answered
Will converting AU to M4R lose quality?
Some. Since au is lossless-oriented and m4r 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 M4R file work?
iPhones accept .m4r only through iTunes or Finder sync and GarageBand export, and every Apple device can play it since the audio is ordinary AAC. Other platforms open the file happily after a rename, though Android sources its ringtones from plain MP3 or OGG instead.
Will the M4R 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.