This section describes related work on broadcast production and control.
Several projects have developed software interfaces to a video production system. NBC's GEnesis project monitors and controls program streams with a software system built with Tcl/Tk [3]. GEnesis provides a graphical user interface to control broadcast schedules that vary over time and region. For example, a live sports event has commercials that vary depending on the location. The system employs a database to store and retrieve schedules, and device controls are accessed with a string protocol over sockets. Operations are implemented by sending commands to conventional broadcast equipment. Both dc and GEnesis control remote devices, but they are solving different problems. Dc concentrates on the production of video streams rather than the scheduling of existing streams.
The Berkeley Multimedia Research Center developed several prototypes before dc. The Software-Only Video Production Switcher project introduced video-effects processes to our production environment [21]. It used remote processes that received and transmitted streams from a studio session. It employed a message protocol to control these remote processes. However, the user interface was hard-coded into the broadcast application and there was no notion of modular services. Moreover, only a single stream was produced from the system. This system was an early prototype for the PSVP effects system.