About Kataribe
Kataribe joins a folder of audio files into one M4B audiobook with chapters, cover art and metadata, ready for Apple Books, Audiobookshelf and other players. It is free, it needs no account, and your audio never leaves your device.
Why it exists
Audiobooks from CDs, public-domain recordings and DRM-free stores usually arrive as dozens of separate MP3s. Music apps shuffle them, forget your place and scatter the chapters. A single M4B file fixes that: the player remembers where you stopped and shows a real chapter list.
Making one has meant installing command-line tools or uploading hours of audio to a website. Kataribe was built to do the whole job in the browser tab.
How it works
Kataribe runs FFmpeg compiled to WebAssembly inside your browser. It accepts MP3, M4A, AAC, WAV, FLAC, OGG and Opus files, reads their tags to suggest the book title, author and chapter names, and puts the tracks in order. When the source is already AAC it is copied without re-encoding, so there is no quality loss. Other formats are encoded to AAC at the bitrate you choose.
Chapter markers, the cover image and the book metadata are written into the finished file. Everything happens on your own machine and nothing is uploaded. The practical limit is your device memory: a very long book builds more comfortably on a laptop than on a phone.
What it does not do
Kataribe is for audio you own. It does not remove DRM, so protected store purchases will not open, and it never hosts, downloads or indexes books.
Who makes it
Kataribe is made by Nathan Stewart at I4C Studio, a one-person product studio that builds developer tools and small, single-purpose web tools. The same person writes the code, the guides on this site and the replies to your email.
The studio's other free browser tools work the same way, on your device with no upload:
How it is paid for
Kataribe is free to use, with no account, no trial and no paid tier. Advertising through Google AdSense covers the hosting. The ads are the only part of the site that involves a third party beyond hosting and aggregate analytics, and the privacy page explains exactly what that means.
Where to start
Found a file that will not convert, or a mistake in a guide? The contact page says how to report it.