3G2 is a digital multimedia container format developed by the Third Generation Partnership Project (3GPP). It can save both video and audio tracks, just like its sister format, 3GP. However, it’s the updated version of the former because it is designed for CDMA (Code Division Multiple Access) mobile phones, whereas 3GP is intended for GSM phones.
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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.