Convert M4B to MP4 — Free Online Converter

M4B is technically an MP4 container with a different file extension and audiobook-specific features (chapters, bookmarks). Converting M4B to MP4 is a near-trivial container relabel — the AAC audio data is identical in both formats. The practical effect is that players and systems recognize the file as generic multimedia rather than an audiobook, enabling upload to platforms that accept MP4 but not M4B.

Many platforms accept MP4 but not M4B: social media, web embedding, CMS uploads, video hosting services, and learning management systems. Converting to MP4 makes audiobook content uploadable to these platforms. Some automated media pipelines only process files with the .mp4 extension. The conversion enables broader distribution of audiobook content outside dedicated audiobook platforms.

FFmpeg performs a stream copy from M4B to MP4. The ftyp brand code changes from M4B to isom or mp42. The AAC audio frames transfer bit-for-bit. Chapter tracks are typically stripped (MP4 supports chapters but most players ignore them). The operation is instant.