Audio Joiner — Merge MP3 & Audio Files
Combine several MP3 or audio files into one. Add your tracks, drag them into order, and join — instantly when the formats match, or re-encoded to MP3 when they differ. No upload, works offline — your audio is merged on your device and never leaves it.
Runs entirely in your browser — your audio is never uploaded.
- No upload Your video never leaves your device — it is processed locally.
- Works offline After the first load it runs with no internet connection.
- No size or daily limits No file caps, no paywalls — only your device memory.
- Private & safe Skip sketchy upload sites; nothing is sent to a server.
How it works
Joining is handled by ffmpeg compiled to WebAssembly and run inside your
browser. The files are written to an in-memory list in the order you set, then combined with
ffmpeg’s concat demuxer. When every file shares the same codec and parameters,
the tool uses a stream copy (-c copy) that simply stitches the data together with
no re-encoding — practically instant and lossless. When the files differ, it re-encodes them all
into one MP3 with the LAME encoder (libmp3lame) at the bitrate you choose, so the
pieces fit together cleanly. Every step runs on your device, so nothing is uploaded, and the
engine is cached after its one-time download (about 9 MB) for offline use.
How to join audio files
- Add two or more audio files with the drop zone above, or drag them onto it.
- Use the up and down arrows to arrange the tracks in playback order.
- Leave the join method on Automatic, or force a re-encode to MP3.
- Press Join audio, then click Download when it finishes.
Same-format joins copy the data and are near-instant even for long files. The re-encode path processes every sample in the browser, so large collections take longer, especially on a phone.
Why join audio locally instead of on an upload site
Online audio joiners upload every file to a server, merge them there and hand back a link — slower over a typical connection, and it exposes your recordings to a third party, often with size caps or paid tiers. Joining in your browser removes the upload step entirely, keeps the audio private, and has no limits beyond your device memory. It also sidesteps a genuine safety problem: in March 2025 the FBI’s Denver field office warned that some free online file tools were being used to spread malware — so keeping the work on your own machine is simply safer.
| Local (this site) | Typical cloud tool | |
|---|---|---|
| Upload required | No | Usually |
| File-size caps | None (device memory) | Common |
| Works offline | Yes, after first load | No |
| Files stay private | Yes — never sent | Sent to a server |
Common uses
Stitching the chapters of an audiobook into one file, combining several voice memos into a single recording, merging the parts of a long mix or DJ set, joining sound effects or jingles end to end, or assembling separate song downloads into one continuous track for a playlist. Arrange the order first so the pieces play exactly as you intend.
More video & audio tools
Frequently asked questions
Is my audio uploaded to join the files?
No. The whole job runs inside your browser with ffmpeg compiled to WebAssembly. Each file you add is read into memory on your own device, joined there in the order you set, and the combined file is written locally for download. Nothing is sent to a server, so there is no upload wait and no copy of your tracks is stored online.
Why is joining sometimes instant and sometimes slower?
When every file shares the same format and encoding settings — for example several MP3s exported the same way — the tool concatenates them without re-encoding (a stream copy), which is essentially instant no matter how long they are. When the files differ in format, sample rate or channels, they cannot simply be glued together, so the tool re-encodes them all to a single MP3, which takes a few seconds to a few minutes depending on total length because every sample is processed in the browser.
Do the files have to be the same format?
No. If they are all the same format the join is instant; if they are mixed — say an MP3, an M4A and a WAV — the tool automatically re-encodes them into one MP3 so they fit together cleanly. You can also force the re-encode path manually if a same-format join produces a file that does not play correctly, which can happen when two files share an extension but were encoded with different settings.
How do I change the order of the tracks?
After adding files, each one appears in a numbered list. Use the up and down arrows on a row to move it, or the ✕ button to remove it. The files are joined top to bottom in exactly the order shown, so arrange them the way you want them to play before pressing the join button.
Is there a limit on how many files or how long?
There is no fixed limit beyond your device’s memory. Because everything is held in the browser, very large collections or very long total durations use more RAM and may be slow, particularly on a phone. For a quick result, joining same-format files (which only copies the data) handles long material far better than the re-encode path.
Does it work offline?
Yes. The site is a Progressive Web App, so it works without a connection after the first visit, and the ffmpeg engine is cached after its one-time download so joining keeps working offline.
All processing happens on Video Tools entirely within your browser. Audio is never uploaded to a server.