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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M4R is a filename extension for AAC format, which is developed by Apple Inc. It is typically used to save custom iPhone ringtones from Apple iTunes. M4R can only be created from iTunes purchased songs and is usually DRM protected. It can open on iTunes, VLC Media Player, Apple QuickTime Player, and more.