Merge M4B files
Combine several M4B audiobooks into one — ideal for multi-part books. Chapters from every file land on a single continuous timeline, right in your browser. Your files never leave your device.
Drop your M4B files to merge, or click to browse
M4B · M4A · two or more files · combined in the order below
How merging M4B files works
Drop two or more M4B files, drag them into order, and the tool reads each file's chapters and length. It then joins them into a single audiobook, shifting every chapter onto one continuous timeline. When the files share the same audio settings they are joined without re-encoding — fast and lossless; otherwise they are re-encoded to a common format so they play back seamlessly. Everything runs locally through a WebAssembly build of FFmpeg — nothing is uploaded.
Merging M4B: common questions
- Does merging keep the chapters from each file?
- Yes. Each file's chapters are shifted onto one continuous timeline, so a book split across "Part 1", "Part 2", and so on becomes a single file with all chapters in order. You can also choose to make each file a single chapter instead.
- How does it join the files — is there quality loss?
- When the files share the same audio settings (which parts of the same book almost always do), they are stream-copied together with no re-encode and no quality loss — and it is near-instant. If the files use different settings, they are re-encoded to a common format so they join cleanly; a notice tells you when that happens.
- Can I set the order of the files?
- Yes. Drag the files into the order you want (or use the keyboard). They are joined top-to-bottom, and the chapter timeline follows that order.
- What about the cover and metadata?
- The merged file uses the first file's cover by default, but you can pick any input file's cover, upload a new image, or remove it. You also set the title, author, narrator, year, and genre for the combined book — prefilled from the first file.
- Are my files uploaded anywhere?
- No. Merging runs entirely inside your browser using a WebAssembly build of FFmpeg. Your audiobooks never leave your device. Open your browser's Network tab while merging to verify there are no uploads.