Add chapters to an MP3
Turn one long audio file into a chaptered M4B audiobook — split evenly, auto-detect chapters from the pauses, or set the times yourself, right in your browser. Your files never leave your device.
Drop a single audio file, or click to browse
MP3 · M4A · M4B · WAV · FLAC · OGG · Opus · one long file → chaptered M4B
How adding chapters works
Drop a single audio file and choose where the chapters go: split the book into equal parts, let the tool detect breaks at the quiet pauses, or enter the times by hand — then edit any of them. The file is re-encoded once to AAC and wrapped in an M4B with your chapter markers, cover, and tags. It stays one continuous file, just with a proper chapter list. Everything runs locally through a WebAssembly build of FFmpeg — nothing is uploaded.
Adding chapters: common questions
- I have one big MP3 with no chapters — can this add them?
- Yes. Drop the single file and set chapter marks three ways: split evenly into a number of chapters (or one every N minutes), auto-detect chapters from the pauses in the audio, or type the times yourself. The result is one M4B with proper chapter markers.
- How does "detect from silence" work?
- It scans the audio for quiet gaps and proposes a chapter break at each pause longer than the threshold you set. It reads the whole file, so it takes a while on long books — and you can always adjust the proposed chapters before converting.
- Does this split the file into separate tracks?
- No. It keeps the audio as one continuous file and adds chapter markers over it, so you get a single tidy M4B. To split an M4B into one MP3 per chapter instead, use the M4B to MP3 tool.
- What files can I use, and does quality drop?
- MP3, M4A, M4B, WAV, FLAC, OGG, and Opus. The audio is re-encoded to AAC at the bitrate you choose (64 kbps mono is the audiobook standard and inaudible for speech), with your chapters, cover, and tags written in.
- Are my files uploaded anywhere?
- No. Everything runs inside your browser using a WebAssembly build of FFmpeg. Your audio never leaves your device. Open your browser's Network tab while converting to verify there are no uploads.