RMVB or RealMedia Variable Bitrate is a Variable Bitrate extension of the RealMedia multimedia container format developed by RealNetworks.
As opposed to the more common RM (RealMedia) container, which holds streaming media encoded at a constant bit rate, RMVB is typically used for multimedia content stored locally. Files using this format have the file extension ".rmvb".
Allegedly, RM (RealMedia) formats typically achieve much more efficient compression than MPEG-4 and therefore have become dominately present on video/music sharing platforms such as BitTorrent, eDonkey and Gnutella. Limited support is available on some media players, generally on the Windows and Linux/Unix.