AAC (Advanced Audio Coding) is a lossy audio format developed by Dolby and Sony Corporation, AT&T Bell Laboratories, and Fraunhofer IIS. During compression, AAC eliminates unnecessary data, making it smaller and easier to stream or download. Today, Apple devices such as iPhones and iPads are the biggest users of the AAC format.
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M4B is an audio filename extension for AAC format, which is developed by Apple Inc. It is mainly used on podcast and audiobook files. Typically, M4B files contain audio and other metadata like images, hyperlinks, and chapter markers. M4B files are DRM copy-protected and can be opened on Apple iTunes and QuickTime Player.