RMVB is a file format with a variable bitrate developed by RealNetworks. Actually it is an improved version of RM format. It gives greater bandwidth to videos that are difficult to compress. The extension keeps a high video definition. RMVB files are very popular in Asia and they are not supported by all popular players, so the easiest way to playback them is to convert them to another most common format.

This format was originally intended for voice compression and is able to change the bit rates of encoded audio data. AMR is actively used for encoding and decoding voice while its being transmitted over network channels. The format allows one to consider network capacity and adapt it to channel loads. Due to this, the voice quality is practically undiminished.