What is a .M4B file?
M4B is an MP4-based audiobook format that supports chapters and bookmarks. Used by Apple Books and audiobook players.
- Did you know
- M4B adds chapter and bookmark support on top of the M4A audio format.
- M4B is the same MPEG-4 audio container as M4A, with a separate extension chosen to flag audiobooks.
- Apple Books and iTunes remember your place in an M4B file, resuming exactly where you stopped.
- It supports chapter markers, letting players jump between sections of a long recording.
- Beneath the audiobook labelling it typically carries ordinary AAC-encoded audio.
- What Analyser shows you
- Inspect the waveform, spectrogram, codec, bitrate, channels, and tags of MP3, WAV, FLAC, M4A, AAC, OGG, and Opus audio, and play Apple Core Audio (CAF) files such as iMessage voice messages, decoded on-device with FFmpeg where the browser cannot.
- Open a .M4B file
- Drag a .M4B file onto the Analyser home page (or tap to pick one). It opens entirely in your browser - nothing is uploaded, there is no account, and it works offline once installed.