Editing RealVideo (section)

==Technology==
The first version of RealVideo was announced in 1997 and was based on the [[H.263]] format. At the time, RealNetworks issued a press release saying they had licensed [[Iterated Systems]]' [[ClearVideo]] technology and were including it as the RealVideo Fractal Codec.<ref>{{Cite news |title= Iterated Systems And Progressive Networks Announce Strategic Alliance |work= Press release |date= February 10, 1997 |publisher= RealNetworks China |url=http://china.realnetworks.com/company/press/releases/1997/iterated.html |url-status=dead | archive-url=https://web.archive.org/web/20031127043109/http://china.realnetworks.com/company/press/releases/1997/iterated.html |archive-date= November 27, 2003 |access-date= August 2, 2013 }}</ref><ref>[http://service.real.com/help/library/guides/rpem/htmfiles/install.htm RealVideo Fractal Codec] Reference to RealPlayer Fractal Codec installation option</ref><ref>Terran Interactive, Inc. (1998) [http://www.siggraph.org/education/materials/HyperGraph/video/codecs/ClearVideo.html Codec Central - ClearVideo], Retrieved on 2009-08-12</ref> However, support for ClearVideo quietly disappeared in the next version of RealVideo.

RealVideo continued to use H.263 until RealVideo 8 when the company switched to a [[Proprietary software|proprietary]] video format. RealVideo codecs are identified by [[FourCC|four-character codes]]. RV10 and RV20 are the H.263-based codecs. RV30 and RV40 are RealNetworks' proprietary H.264-based codecs. These identifiers have been the source of some confusion, as people may assume that RV10 is RealVideo version 10 when it is the first version of RealVideo. RealVideo 10 uses RV40.

RealVideo can be played from a RealMedia file or streamed over the network using the [[Real Time Streaming Protocol]] (RTSP), a standard protocol for streaming media developed by the [[IETF]]. However, RealNetworks uses RTSP only to set up and manage the connection. The actual video data is sent with their own proprietary [[Real Data Transport]] (RDT) protocol. This tactic has drawn criticism because it made it difficult to use RealVideo with other player and server software. However, the [[open source|open-source]] [[MPlayer]] project has now developed software capable of playing the RDT streams.

To facilitate real-time streaming, RealVideo (and RealAudio) normally uses [[constant bit rate]] encoding, so that the same amount of data is sent over the network each second. Recently, RealNetworks has introduced a [[variable bit rate]] form called RealMedia Variable Bitrate ([[RMVB]]). This allows for better video quality, however, this format is less suited for streaming because it is difficult to predict how much network capacity a certain video stream will need. Video with fast motion or rapidly changing scenes will require a higher bit rate. If the bit rate of a video stream increases significantly, it may exceed the speed at which data can be transmitted over the network, leading to an interruption in the video.

RealNetworks says that the RealVideo and RealAudio codecs are not available in source code under the [[RealNetworks Public Source License|RPSL]] license. Source code is available only under [[RealNetworks Community Source License|RCSL]] license for commercial porting to non-supported processors and operating systems. While RealNetworks owns most of the intellectual property for RealVideo and RealAudio, RealNetworks has licensed third-party technology for certain aspects of those codecs. RealNetworks claims that it does not have the right to license that technology under an open-source license.<ref name="helix-producer">Helix Community, [https://helix-producer.helixcommunity.org/Faq.htm Helix Producer Category FAQ] {{Webarchive|url=https://web.archive.org/web/20110726144823/https://helix-producer.helixcommunity.org/Faq.htm |date=2011-07-26 }}, Retrieved on 2009-08-02</ref>