Wikipedia
RealVideo
RealVideo is a suite of proprietary video compression formats developed by RealNetworks – the specific format changes with the version. It was first released in 1997 and is at version 10. RealVideo is supported on many platforms, including Windows, Mac, Linux, Solaris, and several mobile phones.
RealVideo is usually paired with RealAudio and packaged in a RealMedia (.rm) container. RealMedia is suitable for use as a streaming media format, that is one which is viewed while it is being sent over the network. Streaming video can be used to watch live television, since it does not require downloading the entire video in advance. Compression and decompression software for each version are called "codecs".