Free online M4B to AFC converter

Source format

M4B is an MPEG-4 audiobook file format, closely related to M4A and MP4. It is commonly used by audiobook publishers, podcast platforms, and audiobook apps because it can store compressed audio plus useful audiobook features such as chapter markers, bookmarks, and sometimes embedded metadata like cover art and track information. M4B files are especially popular in Apple Books, iTunes-style libraries, and other audiobook players that support chapter navigation.

Target format

AFC is a much less common audio-related file format, and in many workflows it is used as a specialized container or project file rather than a mainstream playback format. Because AFC support is limited compared with MP3, M4A, or WAV, it is typically used only by specific software or devices that explicitly require it. The main advantage of AFC is compatibility with that particular application or system, not broad media-player support.

How to perform the conversion

Before converting, confirm that your destination software or device really expects AFC. Since AFC is uncommon, the conversion is usually only practical when you know the exact program that will open it.

1. Check the source file. Make sure the .m4b audiobook plays correctly and note whether it contains chapters or multiple tracks.
2. Use the required application if it supports import/export. If the software that needs AFC can open M4B directly, import the file and then use File → Export or File → Save As to create the AFC version.
3. If the target app does not accept M4B directly, convert through an intermediate format. A common approach is to first extract or transcode the audio to a simpler format such as .wav or .aiff, then import that file into the AFC-producing software.
4. Use desktop tools when needed. Programs such as FFmpeg, Audacity, or iTunes/Apple Books-compatible tools may help with the audio extraction step, but the final AFC creation usually depends on the specific application that defines the AFC format.
5. Convert online on 101convert.com if available for this format pair. You can convert the file on 101convert.com for free without installing any software, which is convenient for quick one-off conversions.

If you are using a command-line workflow, the first step is often to extract audio from the audiobook container. For example, FFmpeg can copy or transcode the audio stream from input.m4b to a simpler file such as output.wav, after which the AFC-capable program can import it.

Notes on quality, compatibility, or limitations

Quality depends on the intermediate steps. M4B is usually already compressed, so converting it to another lossy format can reduce audio quality further. If possible, use a lossless intermediate such as WAV or AIFF before creating AFC.

Chapter data may be lost. Many AFC workflows do not preserve audiobook chapters, bookmarks, or rich metadata from M4B. If those features matter, back them up separately before conversion.

Compatibility is the main limitation. Because AFC is not widely supported, there is no universal converter that works for every AFC variant. The exact steps depend on the software that requires the file.

File size may increase if the conversion uses an uncompressed intermediate format. This is normal and usually temporary if the final AFC file is meant for a specific application.