RealVideo is a streaming video format developed by RealNetworks.
At one time RealVideo was a de facto standard for anime fansubs, which have been used by anime fans to distribute movies and TV shows to areas where they aren't otherwise available. RealVideo became popular because of its (then) superior quality at exceedingly low bitrates.
RealVideo was originally introduced in 1997 and in 2008 had hit version 11.
The video is normally packed in a RealMedia (.rm) container along with RealAudio. is usually paired with RealAudio and packaged in a container.
The technology is based on a constant bitrate transfer, but RealNetworks has released RMVB which allows for improved variable bitrate transfers. The original RealVideo was based on the H.263 codec up until RealVideo 8 was released and the company moved to its own proprietary video codec.
RealVideo has fallen out of favor in the last few years to FLV and Quicktime and many feel the RealVideo player is bloatware and should never be installed on one's computer.