M4B is a file format used to create audiobooks and podcasts. The MPEG-4 standard is used to encode the content in such a file. In addition to the audio content, an M4B file also stores metadata that allows you to conveniently use its content. These are tabs, links to individual chapters and where the playback of material was last stopped.

The M4B format is used by Apple solutions. Sometimes these materials are secured using the DRM system. This allows you to protect the publisher's rights and copyrights from illegal use of the content.