Join audio files into one
Add two files or forty. They are played back to back in the order shown and written as one file. Mixed formats are fine — different codecs, sample rates and channel counts are reconciled for you.
Join audio files
They play in the order you added them. Add more at any point.
Starting the converter…
The job that makes a server converter painful
Joining is where the no-upload argument stops being a principle and starts being practical. Thirty audiobook chapters, a set of lecture recordings, a three-hour sermon series split into files — that is a gigabyte or more of material. On a converter with a server behind it, every one of those bytes has to travel there first, and services with a server to pay for generally cap free use by file size, by file count, or by jobs per day.
Here nothing travels. The files are read off your own disk, joined in the tab, and handed back. There is no file-count limit because there is nothing to meter.
Mixed formats are handled, and that is not trivial
Recordings gathered over time are rarely uniform. One was made at 44.1 kHz in stereo, another at 22 kHz in mono, a third is a FLAC and the rest are MP3s. Joining those naively produces a file that plays at the wrong speed after the first join, or drops to one channel halfway through, or simply fails.
This decodes everything to a common format first, then writes the result once. It is slower than a pure copy, but it is the thing that actually works. We tested it on exactly that case — 44.1 kHz stereo MP3, 22 kHz mono M4A and 48 kHz stereo WAV, joined into one MP3 of the correct combined length.
| What differs | What is done about it |
|---|---|
| Different codecs | All decoded, then encoded once to the output you chose |
| Different sample rates | Resampled to a common rate, so nothing plays at the wrong speed |
| Mono and stereo mixed | Reconciled, so the file does not collapse to one channel partway |
| Different bitrates | Irrelevant once decoded; the output bitrate is the one you pick |
Order, and the mistake worth avoiding
Files are joined in the order they appear in the list, which is the order you added them. If you select a whole folder at once, that is whatever order your operating system handed them over in — usually alphabetical, which is why chapters named 01, 02, 03 behave and chapters named 1, 2, 10 do not. 10 sorts before 2.
Check the list before converting. Each row shows the filename, and you can remove any of them and add files again in the order you want.
Crossfade
Joining two files can either butt them together — the default, and what you want for chapters or lecture parts — or overlap them so one fades out as the next fades in. The crossfade is available when you are joining exactly two files, which is the case where it makes musical sense. For a long list of chapters, a hard join is correct: you do not want chapter three bleeding into chapter four.
What format to write
- MP3 — the safe answer. Plays on everything, and every podcast app, car and player understands a long one.
- M4A — better audio at the same bitrate, and the format Apple's ecosystem prefers. A good choice for spoken word you will listen to on a phone.
- WAV or FLAC — when the joined file is going into an editor rather than a player. Both are uncompressed or lossless, so nothing is added on top of whatever the sources already lost.
If the parts were lossy, the joined file is a fresh encode of already-compressed audio. Writing it as WAV or FLAC keeps it from getting worse again, but it cannot make it better than the parts were. Where the sources are lossless, choose FLAC or ALAC and nothing is lost at all.
Long jobs
A dozen chapters into one audiobook is a real encode of the full combined length, so expect it to take a while — the engine is single-threaded WebAssembly, not a native tool. The progress bar tracks the whole job. The tab has to stay open, and the ordinary ceiling applies: this warns above 300 MB and refuses above 2 GB, which is the browser's limit rather than ours.
Step by step
Add the files
Select several at once, or add them one at a time. Each shows its own codec, length and bitrate as it loads.
Check the order
They are joined in the order listed. Remove any with the ✕ and add more with the button below the list.
Pick the output
MP3 for maximum compatibility, M4A for efficiency, WAV or FLAC to stay uncompressed.
Download the single file
One file, the full combined length, with the total shown before and after.
About joining audio
How many files can I join?
There is no limit imposed here. Nothing is uploaded and nothing is metered, so joining forty audiobook chapters costs the same as joining two — a longer wait, and nothing else. The practical ceiling is the browser tab's memory.
Learn moreCan I mix formats — some MP3, some M4A, some WAV?
Yes. Everything is decoded to a common format first, so differing codecs, sample rates and channel counts are reconciled rather than producing a file that plays at the wrong speed halfway through. We tested exactly that combination.
Learn moreWhat order will they play in?
The order in the list, which is the order you added them. Watch out for filenames numbered without leading zeros — 10 sorts before 2 in most file pickers. Check the list before converting; you can remove files and re-add them.
Learn moreDoes joining make the audio worse?
The parts are decoded and re-encoded once into the output you chose, so if they were lossy that is another lossy pass. Choosing FLAC or WAV avoids adding anything on top, though it cannot improve what the sources already lost.
Learn moreCan I make an audiobook file with chapters?
This joins the audio into one continuous file; it does not write chapter markers. For a long spoken-word file, M4A is the better container and most players will remember your position in it. The audiobook guide covers what chapter support actually requires.
Learn moreDo the files go to a server first?
No, and that is the point on this page more than any other. Joining is what people do to large sets of files, which is exactly the case where sending everything somewhere first is slowest. Nothing here moves off your machine.
Learn more