What is the AUP file format?
A .aup file contains project data for an Audacity project. Audacity is an open-source audio editing application available on Windows, macOS and Linux.
.aup files use XML format to save project data, storing information about tracks, clips, labels, envelopes and sample-rate settings for each stage of a given project, along with references to audio resource files. Those resource files live in a companion <projectname>_data folder, which holds thousands of small .au PCM audio blocks. The .aup file is only a manifest - it is useless without its matching _data folder and is not a playable audio file.
The .aup format is a legacy format, last used in Audacity 2.4.2 (2020). Since Audacity 3.0 (2021), projects are saved as .aup3, a single self-contained file with no separate data folder. Audacity 3.x still opens old .aup projects and converts them automatically.
Exporting .aup files
Audacity offers an option to export to many popular audio formats such as WAV or MP3. Older versions required the separate LAME codec package to export to .mp3; since Audacity 2.3, LAME is bundled automatically and no additional codec needs to be installed.
Security & safety
RISK: LOWAn .aup is plain-text XML referencing local audio blocks - no executable code, low risk. The real hazard is data loss, not malware: keep the .aup and its <name>_data folder together, and never delete the _data folder thinking the .aup holds the audio. To back up or send a project, zip the .aup and its _data folder together.
Format details
in a nutshellPrograms that open AUP files
Windows1 app
Audacity
Open-source File - Open the .aup (keep the _data folder beside it). Audacity 3.x converts it to .aup3. To get audio, File - Export. 
macOS1 app
Linux1 app
Audacity
Open-source Install from the distro or Flatpak; File - Open the .aup with its _data folder. Technical details
deep spec| Format type | XML text manifest - a pointer file, not a self-contained audio container |
| MIME type | text/xml (also application/x-audacity-project) |
| File signature | <?xml at byte 0; root element <project xmlns="http://audacity.sourceforge.net/xml/"> |
| Companion folder | <projectname>_data placed alongside the .aup, containing the actual .au PCM audio blocks |
| Audio block format | Uncompressed .au (Sun AU) PCM files arranged in a two-level subdirectory tree inside the _data folder |
| Compression | None - both the XML manifest and the .au audio block files are uncompressed |
| Stored sample rate | Defined per-project in the XML; commonly 44,100 Hz or 48,000 Hz, but any rate Audacity supports |
| Manifest file size | Typically a few KB to a few hundred KB; the _data folder holding actual audio can reach tens of MB to several GB |
| Platform support | Windows, macOS, Linux |
| Superseded by | .aup3 (single-file SQLite project) introduced in Audacity 3.0 (2021), eliminating the separate _data folder |
| Developer | Audacity (originally Dominic Mazzoni and Roger Dannenberg; now maintained by Muse Group) |
| XML encoding | UTF-8 |
| Integrity checking | None built-in; project integrity depends on all referenced .au blocks being present in the _data folder |
| Released | 2000 (Audacity 1.0); legacy AUP format used through Audacity 2.x |
| Latest version | Final AUP (XML) format in Audacity 2.4.2 (2020); replaced by .aup3 in Audacity 3.0 (2021) |
| Open standard | Yes · royalty-free |
| Specification | manual.audacityteam.org |
AUP conversions
Community Q&A
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