RealMedia Variable Bitrate (RMVB) is a file format developed by RealNetworks as a variable bitrate extension to the RealMedia multimedia digital container format. RMVB is typically used for media that is stored locally, as it is not designed for streaming, unlike the regular RealMedia container, which is meant to hold streaming media that is encoded at a constant bitrate.
RealMedia Variable Bitrate uses a compression algorithm similar to that used in MPEG-4 Part 10 encoders, such as the famous x264. The compression results in videos with good quality but smaller file size, which makes them suitable for sharing and distribution over the Internet. In fact, for a time, it was very common to see RMVB files on peer-to-peer file sharing platforms such as Azureus, BitTorrent, eDonkey and Gnutella. RealMedia Variable Bitrate is still popular for sharing, although not for streaming, as the videos have good quality and smaller file size compared to other formats.