RealMedia is a multimedia container format created by RealNetworks. Its extension is “.rm”. It is typically used in conjunction with RealVideo and RealAudio and is used for streaming content over the Internet.
Typically these streams are in CBR (constant bitrate).
Recently, RealNetworks has developed a new container for VBR (variable bitrate) streams, named RMVB (RealMedia variable bitrate).
Support of RealMedia is available in a wide variety of multimedia players for different architectures/platforms, including RealPlayer and the Real Alternative codec pack. The open source DAP firmware Rockbox has added support for reading RM containers as of 6 July 2009, although only certain codecs contained in RM files are playable