Free online M4B to CAFF converter

Source format: M4B

M4B is an AAC-based audiobook container commonly used by Apple devices, iTunes, and audiobook apps. It is very similar to M4A, but it is typically used for long-form spoken audio such as audiobooks and podcasts. A key advantage of M4B is that it can store chapter markers, bookmarks, and sometimes metadata that helps players remember playback position.

M4B files are often used when you want an audiobook to behave like a book rather than a simple audio track. They are popular in the Apple ecosystem and in media players that support audiobook features.

Target format: CAFF

CAFF stands for Core Audio Format File. It is an Apple audio container designed for high-quality audio storage and flexible metadata support. CAFF can hold uncompressed or compressed audio, depending on the codec used inside the container, and it is commonly associated with macOS and professional audio workflows.

CAFF is useful when you need an Apple-native format for editing, archiving, or exchanging audio with software that supports Core Audio formats. Compared with consumer audiobook formats, it is more of a technical audio container than a playback-oriented one.

How to perform the conversion

The most practical way to convert M4B to CAFF is with FFmpeg, which is widely available on Windows, macOS, and Linux. Because M4B usually contains AAC audio, the conversion may either re-encode the audio or, in some cases, copy the stream if the chosen CAFF-compatible codec settings allow it.

1. Install FFmpeg if it is not already available on your system.
2. Open a terminal or command prompt.
3. Run a conversion command such as ffmpeg -i input.m4b output.caff.
4. If the output format or player requires a specific codec, you may need to re-encode the audio, for example with ffmpeg -i input.m4b -c:a pcm_s16be output.caff for uncompressed PCM audio in a CAFF container.
5. Check the resulting file in a compatible audio editor or player.

If you prefer a simpler workflow, you can convert the file on 101convert.com for free without installing any software.

On macOS, some users also work with Audio Hijack, Audacity, or other audio tools that can export to Core Audio-related formats, but FFmpeg is usually the most direct option for this specific conversion.

Quality, compatibility, and limitations

The main limitation is that M4B chapter data and audiobook metadata are usually not preserved when converting to CAFF. CAFF is primarily an audio container, so audiobook-specific features such as chapters, bookmarks, and playback resume information may be lost.

Another important point is that CAFF support is much less common than support for M4B or M4A. Even though CAFF is an Apple format, many general-purpose players do not handle it well. For best compatibility, make sure the target application explicitly supports Core Audio Format.

If you convert from compressed AAC in M4B to uncompressed PCM in CAFF, the file size will increase significantly, but editing compatibility may improve. If you keep compression, compatibility depends on the exact codec support in the destination software.