Which entities co-developed the Real-Time Streaming Protocol (RTSP)?
RealNetworks, Netscape, and Columbia University.
The development of the Real-Time Streaming Protocol (RTSP) was a collaborative effort involving significant industry and academic players working toward establishing an interoperable control standard for media servers. Specifically, the protocol was co-developed by RealNetworks, which was a major player in early proprietary streaming solutions, Netscape, a key browser developer, and Columbia University. This partnership was instrumental in creating a signaling protocol designed explicitly to manage media sessions, dictating actions like play, pause, and seek to the media server, which was a capability missing in purely HTTP-based delivery systems of that era.

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Yuriy Reznik - Streaming in 1970s. NVP & ST - YouTube