Free tool
MP3 joiner
This MP3 joiner puts MP3 files end to end in one MP3. When they share a sample rate and channel count, as the chapters of one audiobook usually do, their frames are copied as they are: no re-encoding, no loss, and done in a moment.
- Free
- No re-encoding when the MP3s match
- Nothing is uploaded
Drop your MP3 files here, or Choose your MP3 files
MP3, M4A, WAV, FLAC, OGG, AAC, or the sound of an MP4, MOV or WebM video, up to 1 GB and 2 hours each. Everything happens in your browser; nothing is uploaded.
MP3 encoding by LAME, open-source software.
Joining the segments of a podcast episode? NoteOwl transcribes the finished episode on your Mac and can write show notes from it with its Podcast Show Notes template.
How it works
How do you merge MP3 files?
Choose all the MP3s together, check they’re in the right order, and press Join MP3 files. If they match, the joiner copies their frames into one file without decoding them; the note under the settings tells you which way it will join before you start.
- 1
Choose the MP3s
Select them together in your file picker. Each row shows its length, bitrate, sample rate and channels.
- 2
Check the order
Drag a row by its handle or use the arrows. Chapter 1 at the top plays first.
- 3
Join and download
Straight on, they’re joined without re-encoding when they match. The file is named after the first MP3.
Can you merge MP3 files without losing quality?
Yes, when the MP3s have the same sample rate and number of channels. An MP3 is a run of small frames, so files that match can be joined by copying their frames one after another. Nothing is decoded or encoded again, so the sound can’t change.
We joined three two-minute chapters this way: the result was 6:00 long, a few hundred bytes smaller than the three files together (it has one header instead of three), and a stretch taken from the middle of each chapter was found in it byte for byte. It took about a tenth of a second.
When does an MP3 joiner have to re-encode?
When the files don’t match, or when you ask for something between them. MP3s at different sample rates, or mono beside stereo, can’t share one stream, and a pause or a crossfade adds new sound. Then the joiner decodes everything and writes one new MP3.
- Same sample rate and channels, straight on
- How they’re joinedFrames copied
- QualityExactly the originals
- Different sample rates (44.1 and 48 kHz)
- How they’re joinedDecoded, one new MP3
- Quality128, 192 or 320 kbps
- Mono and stereo mixed
- How they’re joinedDecoded, one new MP3
- QualityStereo throughout
- With a pause or crossfade
- How they’re joinedDecoded, one new MP3
- Quality128, 192 or 320 kbps
| Your MP3s | How they’re joined | Quality |
|---|---|---|
| Same sample rate and channels, straight on | Frames copied | Exactly the originals |
| Different sample rates (44.1 and 48 kHz) | Decoded, one new MP3 | 128, 192 or 320 kbps |
| Mono and stereo mixed | Decoded, one new MP3 | Stereo throughout |
| With a pause or crossfade | Decoded, one new MP3 | 128, 192 or 320 kbps |
Will there be a gap between the joined MP3s?
Only what was already in the files. Each MP3 keeps the silence its encoder put at its start and end, about 0.04 seconds per file in our test, so three two-minute chapters joined to 6:00.12. For a deliberate break, choose a 1 or 2 second pause.
How do you put audiobook chapters in the right order?
Name them so they sort: 01, 02, 03 rather than 1, 2, 10. Files chosen together arrive in the order your file picker lists them, usually by name, so numbered names come out right without touching anything. Otherwise drag rows into place, or use the arrows.
Audiobook chapters
Usually all made by one encoder, so they join without re-encoding.
Podcast segments
Intro, interview and outro recorded apart. Check the intro wasn’t exported at another sample rate.
A recording in parts
A recorder that starts a new MP3 every so often: join the parts back into one.
What can you do with a finished podcast episode on a Mac?
Turn it into text. NoteOwl transcribes an MP3 on your Mac, labels each speaker and can write show notes with its Podcast Show Notes template. It also saves subtitles as an SRT file for the video version of the episode.
FAQ
Questions about joining MP3 files
Does the MP3 joiner upload my files?
No. The MP3s are joined in this browser tab: their frames are read from your disk and written into one new file there, which you then download. The page sent nothing while we joined three chapters, and needs no account.
How do I know whether my MP3s will be re-encoded?
The joiner tells you before you start. The line under the settings says the frames will be copied end to end, or explains why they’ll be decoded and written as a new MP3: different sample rates or channels, or a pause or crossfade you chose.
Can I join MP3s with different bitrates?
Yes, and without re-encoding, as long as their sample rate and channels match. Each frame carries its own bitrate, so a 64 kbps chapter can follow a 128 kbps one in the same file.
How long does it take to merge MP3 files?
Without re-encoding, about as long as reading them: six minutes of chapters joined in well under a second. When they must be re-encoded, a few seconds for each few minutes of sound.
Can I join other formats, such as M4A or WAV?
Not on this page, which is for MP3s. NoteOwl’s audio joiner takes M4A, WAV, FLAC, OGG and MP3 together, in any mix, and writes one MP3 or WAV.
Does the joined MP3 keep the chapters’ tags?
No. The joined file is one new MP3 without title or artist tags. Add them afterwards in your music app or tag editor if you need them.
Keep exploring
More audio editing tools
- Audio compressorMake any audio file smaller in your browser: pick a quality or a size to fit (such as 25 MB for email) and see the size before and after
- MP3 compressorShrink an MP3 by re-encoding it at a lower bitrate in your browser, with the size before and after; only settings that make it smaller are offered
- WAV compressorMake a WAV smaller in your browser: lossless FLAC, a smaller WAV (lower sample rate, mono, 16-bit) or MP3, with the size before and after
- Volume boosterMake an audio file louder in your browser, up to +30 dB, with a limiter that stops it clipping and a preview before you save
Related
- M4A to MP3 converterConvert M4A to MP3 in your browser, iPhone and Mac voice memos included, at 128, 192 or 320 kbps; nothing is uploaded
- AI transcription for podcastersEpisodes imported and transcribed speaker by speaker on your Mac, show notes from the Podcast Show Notes template, SRT subtitles; nothing uploaded
- Export your notesExport meetings, dictations and notes as Markdown or PDF, imported transcripts as text or SRT, or everything as plain files; nothing is locked in
Episodes into transcripts and show notes, on your Mac
Free to download. Runs entirely on your Mac.
macOS 26 or later · Apple Silicon (M1 or newer) · 16 GB memory minimum, 24 GB recommended
About NoteOwl
NoteOwl is private AI meeting notes and memory for the Mac. It captures meetings without a bot joining the call, labels every speaker, writes summaries and action items, and builds a memory of every conversation that you can chat with — fully offline, because the speech recognition and the AI run on the Mac itself. Dictation into any app is free; Pro is a one-time purchase.
NoteOwl pricing: what’s free and what Pro adds
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