AU to M4A Converter

Convert AU (Sun/NeXT AU audio) files to M4A online, for free, with nothing to install.

To convert AU to M4A, select or drop your .au file above, check that M4A is chosen as the output, and click Convert. This conversion runs on our server, and your files are deleted 72 hours later.

What is an AU file?

AU – Sun/NeXT AU audio. AU is the audio format of Sun and NeXT computers, simple and old; Unix tools and some programming libraries still read it. Converting makes a new file: the sound is decoded and written again, so converting from a lossy format never brings back what was lost.

AU Converter →

What is an M4A file?

M4A – MPEG-4 audio (M4A). M4A is audio (usually AAC or Apple Lossless) in an MP4 file, the format of iTunes, Apple Music and iPhone voice memos. Converting makes a new file: the sound is decoded and written again, so converting from a lossy format never brings back what was lost.

M4A Converter →

How to convert AU to M4A

  1. Click Select File, or drop your .au files anywhere on this page. You can add several at once.
  2. Check that M4A is chosen as the output format. On this page it is picked for you.
  3. Click Convert. When a file has to go to our server, the button says Upload and convert instead.
  4. Click Download next to each file when it's done.

AU vs M4A: how they compare

AUM4A
LayoutA stream of soundA stream of sound
EditableIn audio editorsIn audio editors
Created bySun Microsystems, 1992Apple, 2001
Best forUnix programs and scientific toolsMusic in iTunes and on iPhones

Good to know

  • The sound is decoded and written as an M4A file at a fixed quality (192 kbit/s).
  • Tags such as title and artist are kept where the new format has room for them. Only the first audio track is converted; pictures and video are left out.

Frequently asked questions

Is converting AU to M4A free?

Yes. Everyone gets 25 free credits a day, with no account needed. Conversions on our server use one credit per started minute of work, so most cost a single credit. Credits reset at midnight UTC.

Are my AU files uploaded anywhere?

This conversion runs on our server, because converting audio needs ffmpeg, which does not run in a browser. Your file is sent over an encrypted connection, and both it and the result are deleted 72 hours after the conversion. The server has no internet access while it works on your file.

How large can the AU file be?

Up to 1 GB per file. This conversion runs on our server, which accepts files up to that size.

Will the M4A look the same as the AU?

It sounds very close: the sound is encoded again as M4A at a fixed quality, so a little detail is lost, and tags such as title and artist are kept where M4A has room for them.

Can I convert several AU files at once?

Yes. Add as many files as you like; they are converted one after another, and each one gets its own Download button.

How long does converting AU to M4A take?

In our tests a one-hour WAV recording became an M4A file in about 46 seconds. A song of a few minutes takes a few seconds, and most conversions cost a single credit.

Convert AU to other formats

Convert other files to M4A

All audio formats

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