Abstract: A multiple video preview system for a production video switcher or digital effects device compresses a plurality of input video signals taken from various points along a video path through the switcher or effects device. The compressed input video signals are stored in a display memory in respective designated regions. The display memory is read out in a raster scan manner. The readout of a portion of the display memory occurs simultaneously with the storing of the compressed input video signals occurs in another portion of the display memory to provide a realtime video output signal that includes each input video signal in a compressed form. The video output signal is input to a monitor to display the input video signals simultaneously.

Abstract: A video production switcher comprises a background mixer, a program bus for connecting a selected video source to the program input of the background mixer, and a downstream key mixer and a preview mixer each having a background input and a key fill input. The key fill inputs of the downstream key mixer and the preview mixer are each connected to receive the same key fill video signal. Each of the latter mixers combines the signal present at its background input with the signal present at its key fill input in dependence on the signal present at its control input. A preview selector connects the background input of the preview mixer selectively either to a second video source, or to the program bus, or to a third video source, and a key control switch connects the transition control input of the preview mixer selectively either to a reference potential level or to a key signal source.