RealVideo is a suite of proprietaryvideo compression formats developed by RealNetworks – the specific format changes with the version. It was first released in 1997 and was 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 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".
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. 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 video format. RealVideo codecs are identified by 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 actually 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, 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 protocol. This tactic has drawn criticism because it made it difficult to use RealVideo with other player and server software. However, the open sourceMPlayer project has now developed software capable of playing the RDT streams. To facilitate real-time streaming, RealVideo 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. 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 RPSL license. Source code is available only under 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 rights to license that technology under an open source license.
RealVideo Players
The official player for RealVideo is RealNetworks RealPlayer SP, currently at version 15, and is available for various platforms including Windows, Macintosh, and Linux. Several other players exist, including MPlayer and Media Player Classic. Many of these rely on the dynamically linked libraries from the official RealPlayer to play the video, and thus require RealPlayer to be installed. However, the open source ffmpeg library can play RealVideo and does not require RealPlayer or any parts thereof. The latest version of RealPlayer that can run on Windows 9x is RealPlayer 8; but this version can be easily modified to play RealPlayer 9 and 10 files, by the manual addition of just three.dll files, from Microsoft's free distribution of RealPlayer 10, that aren't included in RealPlayer 8 Basic. RealNetworks has also developed the open source Helix player, however support for RealVideo in the Helix Project is limited because RealNetworks is still keeping the codecs proprietary. RealPlayer does not record RealVideo streams, and RealNetworks has advertised this feature to content owners such as broadcasters, film studios, and music labels, as a means of discouraging users from copying video. However, other software exists which can save the streams to files for later viewing. Such copying, known as time-shifting, is legal in most countries.
rv20: RealVideo G2 and RealVideo G2+SVT, also based on h.263. SVT is a feature that allows for decoding at a lower framerate on low-end machines.
RV30
rv30: RealVideo 8, suspected to based largely on an early draft of H.264
RV40
rv40: RealVideo 9, suspected to be based on H.264
rv40: RealVideo 10, aka RV9 EHQ. This refers to an improved encoder for the RV9 format that is fully backwards compatible with RV9 players – the format and decoder did not change, only the encoder did. As a result, it uses the same FourCC.
RV60
rv60: RealMedia HD, suspected to be based on HEVC. In April 2018, RealNetworks posted test results of encoder speed and compression efficiency. Their tests compared RealMedia HD to HEVC, H.264 and VP9 encoders. Results claimed RealMedia HD provided higher compression than HEVC at higher perceived quality levels. RealMedia HD was also purportedly faster than x265 and VP9 at comparable complexity settings.
The newest version of RealPlayer can play any RealVideo file, as can programs using FFmpeg. Other programs may not support all video compression formats. In addition to decoder code for up to RV50, FFmpeg also contains open-source code for RV10 and RV20 encoders.
