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.
F4V is a filename extension for Flash Video (FLV) container format. It supports H.264 (MPEG-4 AVC) video codec compression standard, which is known to offer significant compression. FLV videos come in multiple formats apart from F4V, including F4P, F4A, and F4B. Also, it opens on Adobe Flash Player 6 or later and Windows Media Player.
Windows Media Player Adobe Flash Player 6 or later Media Monkey