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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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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