.AU File Extension

When you create or import an audio file into an Audacity project, Audacity automatically converts the file into an AU file. Each project's AU files are stored in that project's folder, which is named myproject_data.

The myproject_data folder also contains your project's AUP file, which is named myproject.aup. When you open your AUP file in Audacity, Audacity automatically searches for and loads the AU files your project includes. If you've moved an AU file that was previously stored in the myproject_data folder, Audacity will show an error message when you open your AUP file.

After you've finished editing your Audacity project, you can export the audio the project contains as an .MP3, .WAV, .M4A, or other common audio file. This is the easiest way to convert the audio saved in an AU file into an audio file that can be played in other audio players.

NOTE: As of version 3.0, Audacity no longer saves AU files that users can access. Instead, Audacity saves all of a project's files within a single .AUP3 file, instead of within a myproject_data folder.

AU files are not meant to be opened individually. Instead, you should open the Audacity (cross-platform) project that uses your AU file. To do so, select File → Open... from Audacity's menu bar. Then, open the AUP file that is stored alongside your AU file, in your project's myproject_data folder.