Merge MP3 Files

How to merge MP3 files

1. Press Choose MP3 files and select the files. You can pick several at once; choosing again adds to the end of the list.
2. Set the order with the ↑ and ↓ buttons. The top file plays first. Remove a file with ✕.
3. Optionally add silence between files (1–3 seconds), then press Merge MP3. Listen to the result right on the page and save it with Download merged.mp3.

The start times under the result show where each original file begins in the merged file. Paste them into a YouTube description as chapters or use them as a table of contents for a lecture.

How lossless MP3 joining works

An MP3 is a chain of small frames, each about 26 milliseconds long. MP3s with the same sample rate (for example 44.1 kHz) and channel layout (stereo or mono) can simply have their frames placed one after another, and the result is a valid MP3. Because nothing is decoded and compressed again, the quality is identical to the originals and even an hour of audio takes seconds. A new header frame with the total length and a seek table goes in front, so players show the right duration and can jump anywhere.

Different bitrates (say 128 kbps and 320 kbps) are fine as long as the sample rate and channels match; the result is a variable-bitrate (VBR) MP3 that plays in any normal player.

Good uses

• Lecture and meeting recordings: voice recorders often split a session into chunks. Join them to listen in one go or to upload to a transcription service.
• Audiobooks and podcasts: combine chapter files into one file that is easy to resume.
• Event playlists: put the songs for a ceremony or show in order with 2–3 seconds of silence between them so nobody has to skip tracks live.

Recordings often contain private conversations. This tool never uploads them; everything happens on your device.

Things to know

• Tiny gaps at the joins: MP3 encoders add a few dozen milliseconds of padding at the start and end of every file. Joining frames keeps that padding, so a gapless live album may show a faint seam. With speech or separate songs you will rarely notice.
• Titles and cover art (ID3 tags) are dropped, because each original has its own title that wouldn't fit the merged file. Add new tags in your music player or a tag editor if you need them.
• File size: lossless joining is light, but re-encoding decodes one file at a time into memory. On a phone, keep each file under about an hour; use a computer for longer ones.
• Re-encoding can only read formats your browser supports (usually MP3, M4A, AAC, WAV and OGG). DRM-protected files can't be processed.

FAQ

Are my files uploaded?

No. Files are never sent to a server; they are processed in your browser and disappear from memory when you close the page. The only download is the MP3 encoder (lamejs), and only when re-encoding is needed.

How many files can I merge?

There is no limit. When the MP3s share a format, several hours of audio is no problem on a computer.

Does merging reduce quality?

Not when the MP3s share a format: they aren't re-encoded. When they differ, the audio is compressed once more, which loses a little; at 192 kbps or higher most people can't hear the difference.

Can I merge M4A or WAV files too?

Yes. If any file isn't an MP3, the browser decodes everything and encodes one MP3, so voice memos saved as M4A can go in the same list.

Sources

• MP3 encoder for the browser, a port of LAME: lamejs (GitHub)
• Audio processing reference: FFmpeg documentation

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