Merge Audio Files into One: combine MP3, M4B and M4A, free

Where it runs

Works in a current Chrome, Edge, Firefox or Safari, on Windows, Mac, Linux and Chromebook computers, Android phones, iPhones and iPads. Nothing to install, no account.

The first file loads the audio engine (ffmpeg, about 31 MB) once, and your browser keeps it. Very long books are easiest on a computer, which has more memory than a phone.

4 simple steps.

Drop your files

Any mix of MP3, M4A, M4B, FLAC, WAV, OGG or Opus, or a whole folder. They sort in natural order.

Put them in order

Drag to reorder, sort by name or reverse. Name the chapter each file starts.

Pick MP3 or M4B

MP3s with matching settings join in original quality, in seconds. Anything else is re-encoded.

Download one file

One MP3 or M4B with a chapter at each file, the cover and the book’s tags.

Merging M4B parts into one book

Long audiobooks often come as two or three M4B files, each with its own chapters. Drop the parts in order and keep Keep each file’s own chapters ticked: every chapter of every part is kept, moved to where its part now starts in the joined book, so part 2’s first chapter starts right where part 1 ends. Files without chapters still get one chapter each. Check the result on the ribbon before you merge.

Joining without re-encoding

An MP3 is a chain of small, self-contained frames. When every file uses the same sample rate and the same number of channels, the frames of one file can follow the frames of the next, so the files are joined exactly as they are. Nothing is decoded or compressed again, which is why it is lossless and fast.

When the files don’t match, for example a 48 kHz stereo file in a book of 44.1 kHz mono files, joining the frames would produce a broken file. The merger tells you why and re-encodes everything to one consistent format instead.

MP3 or M4B?

	One MP3	One M4B
Plays on	Almost every device and car stereo	Apple Books, BookPlayer, Audiobookshelf, Smart AudioBook Player
Chapters	ID3 chapters (podcast and audiobook apps)	Standard audiobook chapters
Remembers your place	Depends on the app	Yes, in audiobook apps
Lossless join	Yes, for matching MP3s	No, always encoded to AAC

Building a finished audiobook? The MP3 to M4B maker adds more control over chapters and book details, and the metadata editor sets the cover and tags afterwards.

Questions, answered.

How do I merge MP3 files into one?

Drop the MP3s (or the folder they are in), check the order, and press “Merge into one MP3”. When the files share a sample rate and channel count, they are joined frame for frame without re-encoding, which keeps the original quality and takes only seconds even for a whole book.

Will merging lower the quality?

Not with “Original quality”. The MP3 frames are copied exactly. If the files differ (for example, some are 44.1 kHz and some 48 kHz, or you choose M4B), the audio is re-encoded at the quality you pick, which is clear for speech even at 64 kbps.

Can I merge files of different formats?

Yes. Mix MP3, M4A, FLAC, WAV, OGG and Opus freely. They are decoded and encoded together into one MP3 or M4B.

Does the merged file have chapters?

Yes, unless you untick it. Each file starts a chapter, named from the list, or, when the files have chapters of their own, those are kept and moved into place. MP3s get ID3 chapters, read by many apps; M4B gets standard audiobook chapters. Fine-tune them afterwards in the chapter editor.

How do I merge M4B files into one?

Drop the M4B parts in order (part 1, part 2…) and keep “Keep each file’s own chapters” ticked. You get one M4B with every chapter of every part, each moved to where its part now starts. The audio is re-encoded once, at the quality you pick.

What is the difference from the MP3 to M4B maker?

This tool combines any files into one MP3 or M4B, joins MP3s without re-encoding, and keeps the chapters of M4B parts. The MP3 to M4B maker binds a folder of chapter files into a finished M4B, with more control over chapters and book details.

Are my files uploaded?

No. Merging happens inside your browser and the files never leave your device.