Convert .aup4 to MP3 online
Turn an Audacity 4 project into an MP3 without opening Audacity — or without having it installed at all. The project is decoded and encoded on this page; the file never leaves your device.
How do I convert an .aup4 file to MP3?
Drop the .aup4 file on this page. It is an SQLite database holding the project's audio as raw sample blocks; the page reads those blocks, lays the clips out on their tracks exactly as Audacity saved them, mixes the tracks to stereo, and encodes the mix to MP3 in your browser. Nothing is uploaded and Audacity does not need to be installed. If you do have Audacity 4, File then Export Audio then MP3 does the same job with its effects rendered.
Drop the .aup4 (or .aup3) file. Nothing is uploaded.
Check the track list and play the mix to confirm it is the right project.
Pick a bitrate and download the MP3 — free for projects up to 256 MB.
Need each track as its own file, or a session over 256 MB? That is Pro.
Convert .aup4 to MP3 online
Search for an Audacity project converter and the results are file-identification pages that stop at "open it in Audacity and export", plus articles selling desktop converters that cannot read the format either. That is fine when Audacity is on the machine in front of you. It is not fine on a Chromebook, a locked-down work laptop, a phone, or a project someone else sent you — and since Audacity 4.0 it is not fine on any machine still running Audacity 3, which cannot open .aup4 at all.
This page reconstructs the timeline from the project database and encodes the mix to MP3 in a Web Worker, so the conversion finishes before an upload would have.
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.
What happens between the project and the MP3
Converting a project is not a format translation, because there is no audio stream inside to translate. The audio lives in the `sampleblocks` table as raw PCM in one of three formats, identified by a code that packs the sample width into its upper bits: 0x00020001 for 16-bit, 0x00040001 for 24-bit stored in four-byte integers, and 0x0004000F for 32-bit float.
Rebuilding the timeline comes first. Each clip records where its sequence starts on the timeline, how much is trimmed from each end, and an amplitude envelope as a list of control points. Each sequence lists its blocks in order with the sample offset each one begins at. Waveward walks that structure, converts every block to float, applies the envelope and the track's volume and pan, and sums the tracks.
Only then is there something to encode. The mix is passed to a LAME MP3 encoder compiled to JavaScript, which runs in the same worker — so the whole conversion is CPU work on your machine, with no server in the path. The port takes 16-bit integer input, so the mix is rounded to 16-bit first — multiplied by 32768, rounded, clipped, no dither — which is one place this differs from Audacity: its own MP3 export hands LAME 32-bit float samples and lets the encoder quantise.
- Input
- .aup4 (Audacity 4.0+) and .aup3 (Audacity 3.0–3.7)
- Output
- MP3 at 128, 192, 256 or 320 kbps, constant bitrate
- Sample rate
- The project's own rate is kept (44.1 or 48 kHz typically)
- Scope
- Stereo mix free; per-track and per-clip files with Pro
- Effects
- Clip gain and envelopes applied; realtime plugins not rendered
- Size limit
- Stereo mix free up to 256 MB; larger exports with Pro. A project too large to hold in memory is read from the file a piece at a time and exported the same way
- Encoder input
- 16-bit integers, rounded without dither; Audacity's export feeds LAME 32-bit float
New to the format? What an .aup4 file is, table by table — and how it differs from .aup3.
Sources
Where the facts on this page were checked. Audacity's code is cited at the tagged release it was read from.
- ExportMP3.cpp, Audacity 3.7.9 — Audacity's MP3 export mixes to floatSample and calls lame_encode_buffer_interleaved_ieee_float (or lame_encode_buffer_ieee_float for mono), so LAME receives 32-bit float samples rather than 16-bit integers.
- Dither.cpp, Audacity 3.7.9 — 16-bit conversion uses one constant both ways, CONVERT_DIV16 = 1 << 15: an integer is read as n / 32768, and a float is stored as lrintf(f × 32768) clipped to −32768…32767. The two dither settings default to none (real-time) and shaped (high-quality).
Converting this file
Q. Audacity saved my recording as .aup4, not .mp3. Can I just rename it?
No. Saving in Audacity 4 writes the project, and an .aup4 is an SQLite database: its first 16 bytes are the text "SQLite format 3" and a zero byte, and the recording sits inside as separate blocks of uncompressed samples plus a document saying where each clip goes. Renaming changes only the label, so a player or phone still finds no MP3 audio in it. An MP3 has to be mixed and encoded from those blocks — in Audacity 4 that is File then Export Audio then MP3, which leaves the project as it is, and without Audacity it is what this page does when you drop the .aup4 here. If the file has already been renamed, rename it back to .aup4: nothing inside it was changed.
Q. Which bitrate should I pick?
320 kbps for music or anything you will edit again; 128 kbps is plenty for spoken word and a quarter of the size. All four options are constant bitrate.
Q. Will the audio match what I hear in Audacity?
For an unprocessed project, yes: the same samples, clip positions, trims, volume, pan and amplitude envelopes Audacity saved are used. Realtime effects and master-track effects are not rendered, so a project whose sound depends on them should be exported from Audacity instead. The page tells you how many effects a project has as soon as it opens.
Q. I want WAV, not MP3.
Use the AUP4 to WAV page — same engine, 16-bit PCM or 32-bit float, with no encoding loss.
Q. My file ends in .aup, .aup3 or -wal, not .aup4. Can it still become an MP3?
That depends on which of the three it is. An .aup3 file converts here exactly like an .aup4: it is the same SQLite design, and this page accepts both. A file ending in -wal is not a project but SQLite's write-ahead log, kept beside a project that Audacity has open or did not close cleanly; leave it next to the project, let Audacity open the project once so the log is merged in, then drop the project file itself. A plain .aup is an Audacity 1.x or 2.x project, a small XML file whose audio lives in a separate _data folder, so the file alone holds no audio for any converter to turn into an MP3 — open it in Audacity 3.7 and save it as .aup3 first, because Audacity 4 cannot import it.
Free to open, play and export the stereo mix for projects up to 256 MB; larger projects still open and play free, and downgrading to .aup3 is free up to the same size. Recovery, per-track stems, and exports or downgrades above that size are a one-time $19 license — no subscription, no recurring fees.
Every job an Audacity project needs
Same local-first engine, one page per task.