Free online M4B to VOX converter

Source format

M4B is an MPEG-4 audiobook container, closely related to M4A and MP4. It is used mainly for audiobooks, long-form spoken content, and podcasts, especially in Apple ecosystems and audiobook players that support chapter markers and playback position saving. M4B files usually contain compressed audio such as AAC, and they may include chapters, metadata, and bookmarks.

Target format

VOX is a speech-oriented audio format associated with Dialogic/OKI ADPCM compression. It is designed for voice recordings and other low-bandwidth spoken audio. The main advantages of VOX are its small file size and suitability for simple voice playback systems. It is not intended for high-fidelity music, but it can be useful when compatibility with older telephony or voice applications matters.

How to perform the conversion

The most reliable way to convert M4B to VOX is with FFmpeg, because it can decode the audiobook container and re-encode the audio into the VOX-compatible codec. If you only need a quick conversion, you can also use the built-in converter on 101convert.com for free without installing software.

Using FFmpeg from the command line:

1. Install FFmpeg on your computer.
2. Open a terminal or command prompt in the folder containing your file.
3. Run a command such as ffmpeg -i input.m4b -acodec adpcm_ima_oki output.vox.
4. Check the output file in a VOX-compatible player or editor.

If your FFmpeg build does not accept adpcm_ima_oki for VOX output, try a different VOX-compatible ADPCM encoder supported by your build, or convert first to a WAV file and then to VOX with software that explicitly supports VOX export.

In a desktop audio editor that supports VOX export, the workflow is usually:

1. Open input.m4b.
2. Choose File → Export or File → Save As.
3. Select VOX as the output format.
4. Save the file as output.vox.

Notes on quality and limitations

M4B to VOX is a lossy conversion. Because M4B audiobook audio is often already compressed, converting it again to VOX will reduce quality further. This is usually acceptable for speech, but it is not ideal if you want to preserve audiobook fidelity.

Important limitations include:

• Chapter markers, bookmarks, and rich metadata in M4B are typically not preserved in VOX.
• VOX support is limited in modern players and editors, so compatibility should be checked before converting.
• VOX is best for mono voice audio; if the source is stereo, it may need to be downmixed.
• Because VOX is a specialized format, some tools may require an intermediate format such as WAV before export.

If your goal is simply to listen to the audiobook on a device that supports VOX, conversion can work well. If you need to keep chapters, metadata, or better audio quality, a more common target such as MP3, WAV, or M4A is usually a better choice.