3GP is a digital media container format developed by the Third Generation Partnership Project (3GPP). It stores both audio and video streams that are transmitted via 4G, 3G, and 2G mobiles phones. Here, the video format is saved in H.264/H.253 codec, while audio is streamed in AAC-LC, HE-AAC v1, AMR-NB, AMR-WB, AMR-WB+, or Enhanced aacPlus.
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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.