What is an .aup4 file?
An .aup4 file is the project format Audacity 4.0 introduced on 3 September 2026. It is one SQLite database holding your audio as thousands of small blocks plus a compact document describing the tracks. Here is what is inside it, what changed from .aup3, and what can open one.
What is an .aup4 file and what opens it?
An .aup4 file is an Audacity 4 project: a single SQLite database that holds your audio as immutable blocks of raw samples plus a binary-encoded XML document describing tracks, clips, trims and envelopes. Audacity 4.0 and newer opens one natively; Audacity 3 cannot, because both the database stamp and the document's format version are newer than it accepts. No media player can open one, because there is no continuous audio stream inside. A browser tool that understands the format, or Audacity 4 itself, is what reads it.
.aup3 vs .aup4
| .aup3 | .aup4 | |
|---|---|---|
| Written by | Audacity 3.0 to 3.7 | Audacity 4.0 and newer |
| Opens in | Audacity 3 and Audacity 4 (4 converts it to .aup4 on open, one way) | Audacity 4 only — Audacity 3.7 refuses it |
| Container | SQLite 3 database | SQLite 3 database (same design) |
| Database version stamp (user_version) | The Audacity 3 build that saved it, e.g. 3.7.9 | The Audacity 4 build that saved it, e.g. 4.0.0 |
| Document version attribute | 1.3.0 — unchanged since the .aup era | 2.0.0 |
| Tables | project, autosave, sampleblocks | project, autosave, sampleblocks, plus project_history (earlier saves) |
| Audio storage | Immutable sample blocks: 16-bit, 24-bit in four bytes, or 32-bit float | Identical — the blocks are the same bytes |
| Clip fields | Offset, trims, envelope; stretch ratio and pitch shift from 3.4 | Adds group id, clip tempo, a stretch-to-project-tempo flag and selection state |
| Colour | A palette index (colorindex) on the track | A palette index on every clip as well; pre-release 4.0 builds wrote a hex color string, which the release does not |
| Unsaved working copy | .aup3unsaved | .aup4unsaved |
| Going back | Not needed | Rewrite the two version stamps and drop the Audacity 4 fields; the audio is untouched |
Drop any .aup4 or .aup3 project to see what it holds.
Read the track list, sample rate, block count and stored format.
Play the mix and export it if that is all you needed.
Follow the links below to convert, downgrade or recover the project.
What is an .aup4 file?
If you have just updated Audacity and your projects have a new extension, nothing is wrong: Audacity 4 opens .aup3 projects and converts them to .aup4 as it does so, leaving the original file untouched. The conversion is one way, though, and that is the part worth knowing before you save. This page explains the format itself, and the tool above will open either version so you can hear what a file contains before deciding anything.
On a Mac? Audacity's own recovery utility only gained a macOS build in January 2026, and it is still a terminal program that asks for about four times the project's size in free space. Everything on this page runs in the browser instead, on any operating system.
Inside the file, table by table
`project` holds two blobs: a dictionary that assigns a two-byte id to every element and attribute name used in the document, and the document itself as a stream of typed tokens referencing those ids. It is XML in structure — a `project` root, `wavetrack` children, `waveclip` and `sequence` below them — but stored in a form that is fast to write after every edit.
`autosave` has the same two columns and holds the state of the project including unsaved changes. When Audacity starts and finds a row there, it offers to recover. A cleanly saved project leaves the table empty.
`sampleblocks` is where the audio lives: a row per block with the sample format, three summary statistics, two pre-computed waveform summaries at different zoom levels, and the raw samples. The summaries are what makes Audacity's waveform draw instantly on a long project, and they are why a viewer can show a waveform without decoding every sample.
`project_history` is new in Audacity 4: a few generations of the document with the time each was saved, so a project whose current document has gone bad can be rolled back to a previous one without touching the audio.
- Extension
- .aup4 (Audacity 4.0+) · .aup4unsaved while editing
- Container
- SQLite 3, with the Audacity application id in the header
- project / autosave
- Dictionary blob plus a binary token document
- sampleblocks
- Raw samples, per-block statistics, two waveform summaries
- project_history
- Earlier saved documents, newest first (Audacity 4)
- Sample formats
- 16-bit, 24-bit in four bytes, or 32-bit float
- Predecessors
- .aup3 (Audacity 3.0–3.7) · .aup plus a _data folder (Audacity 1–2)
Sources
Where the facts on this page were checked. Audacity's code is cited at the tagged release it was read from.
- ProjectFileIO.cpp, Audacity 3.7.9 — The AUDY application id and the packed user_version stamp in the database header, AUDACITY_FILE_FORMAT_VERSION 1.3.0, and the refusal of any project whose version stamp is newer than the running build.
- ProjectFileIO.cpp, Audacity 4.0.0 — AUDACITY_FILE_FORMAT_VERSION 2.0.0, and the project_history table, which keeps the last ten saved documents (kProjectHistoryDepth).
- ProjectSerializer.cpp, Audacity 4.0.0 — The binary XML stream: a dictionary of two-byte name ids and the 17 field types (16 in Audacity 3, plus the blob type Audacity 4 added). Strings are stored in the writing platform's native width, two or four bytes per character.
- WaveClip.cpp, Audacity 4.0.0 — The clip attributes Audacity 4 writes: offset, trims, stretch and tempo fields, groupId, clipTempo, clipStretchToMatchTempo, isSelected, and a per-clip colorindex.
- SqliteSampleBlock.cpp, Audacity 3.7.9 — The sampleblocks columns — sampleformat, summin, summax, sumrms, summary256, summary64k, samples — and silence encoded as a non-positive block id.
- SampleFormat.h, Audacity 3.7.9 — The three sample formats and their codes: int16 0x00020001, int24 0x00040001, float 0x0004000F, with the byte width packed into the upper sixteen bits.
- SQLite database file format — The database header layout: user_version at byte offset 60 and application_id at byte offset 68.
- Audacity 4.0.0 release notes — The .aup4 format, the one-way conversion of .aup3 projects, and the features not in 4.0.
- audacity-project-tools README (Audacity) — Blocks of up to 1 MB holding about five seconds of mono audio at default settings, never updated in place, so block ids are not contiguous within a track.
- Audacity pull request 11985: decode command-line arguments as UTF-8 — Audacity 4.0.0 on Windows mangles a project path containing characters outside the system ANSI code page before opening it, so the project is reported as unreadable or missing; the file is intact, and macOS and Linux are unaffected. Approved 10 September 2026, not merged as of 14 September.
- Audacity issue 12124: an .aup3 with a Japanese name fails in Audacity 4 on Windows 11 — The same refusal on an existing .aup3 opened for conversion; renaming the file to ASCII made it open and convert.
- Audacity pull request 12115: fix codepage conversion issues — The maintainers' wider Windows code-page fix (recent-files records, metadata, export errors, preset names, ffmpeg path), approved 11 September 2026 and not merged as of 14 September; it does not change the command-line parser.
Questions about the format
Q. Is .aup4 different from .aup3 internally?
The storage design is the same — an SQLite database with a document table and a sample-block table. Audacity 4 raised the format version, added a table of earlier saves, and added clip fields: groups, a per-clip tempo, a stretch-to-tempo flag, a selection flag, and a colour index on each clip.
Q. Can I convert .aup4 back to .aup3?
Not in Audacity — the conversion is one way. The downgrade page here rewrites the two version stamps Audacity 3.7 checks and drops the fields it has never seen, keeping the audio unchanged.
Q. What is an .aup4unsaved file?
The same database, written while you work. Audacity keeps unsaved changes in the file's autosave table and names the temporary file with that extension; after a crash it offers to restore from it. This page reads those too.
Q. Why is my project file so much larger than the audio?
Because sample blocks are never edited in place. Every change writes new blocks and leaves the old ones behind until the project is compacted, so an afternoon of editing can multiply the file size. Rebuilding a project here drops every block no clip references.
Q. Why does Audacity 4.0.0 on Windows say my .aup4 cannot be read or found?
Check the path before suspecting the file. Audacity 4.0.0 on Windows decodes a project path passed on the command line with the system ANSI code page instead of UTF-8, so a file name or folder containing Cyrillic, Japanese, Hebrew or accented characters is mangled and the project is reported as unreadable or missing — an accented parent folder is enough, and an .aup3 you are opening for conversion fails the same way (issue 12124: 録音テスト.aup3 refused, test.aup3 converted). The parser fix is Audacity pull request 11985, approved on 10 September 2026; the maintainers' broader code-page fix, pull request 12115, was approved on 11 September. As of 14 September neither is merged and 4.0.0 is still the newest release, so until one ships, move the project to an ASCII-only path or open it from File → Open with no other project open. The file itself is fine, and opens here regardless of its path.
Free to open, play and export the stereo mix for projects up to 256 MB; larger projects still open and play free. Recovery, downgrading, per-track stems and exports above that size are a one-time $19 license — no subscription, no recurring fees.
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