RM (Real Media) is a multimedia format developed by RealNetworks. It features a .rm filename extension and is typically multiplexed with RealAudio and RealVideo when streaming content online. The stream is usually in constant bitrate (CBR), although a file container for variable bitrate (VBR) is now available, called Real Media Variable Bitrate (RMVB).
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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.
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