|Video switcher (video mixer)|
|Saturday, 11 November 2006|
Video switcher or multiplexer has been in use for inputting a plurality of video signals such as video outputs from a plurality of video cameras and dividing per channel the signal in time units such as frames and fields to multiplex the signals and outputting the signals to video recording apparatus such as a VTR, or inputting a multiple video signal generated by video recording apparatus and outputting the signal per channel onto a monitor. A video switcher multiple-records images picked up by a plurality of cameras on a single video cassette recorder (VCR) one frame by one frame in turn. During a multiple recording, a channel code is input by a frame switcher to discriminate each image. To display a user desired channel image on a monitor according to the channel, the channel code input by the frame switcher should be reproduced. In television programming, video switchers receive video input signals from various video sources and direct to the switcher outputs for transmission (or recording) picture images from selected sources. The video sources can include network feeds, satellite feeds, cameras, receivers and recorders. Switching can be done manually by an operator or automatically by programming the switcher to perform a plurality of operations in an predetermined sequence. Transitions can include cuts, fades, mixes and combinations thereof. The transitions controlled using a video switcher or video effects switcher may involve a partial change or a full span change over a time period of more than one video frame, from one video input signal to another. Typical switched effects are the "wipe" and the "mix," and other effects of a similar nature are also possible. A wipe is the insertion of one video signal into another, where the insertion is a predetermined shape, usually a geometric pattern. A mix is a comparable time-varied transition where the full frame of video dissolves into a new frame.
Within the past few years, the use of digital effects to manipulate video signals has increased dramatically in the field of television, and has resulted in a myriad of special effects which, in turn, are of particular interest to television broadcasting facilities and video post production studios. Since switchers have long been used for generating analog effects and otherwise manipulating video signals, it follows that the desirability for supplying digital special effects via a video switcher also has increased dramatically. With advancement of digitization of the video switcher, Digital effects interfaces have been developed which allow coupling a digital effects unit to a video switcher to supply various digital special effects via the switcher. Not only the effect to merely carry out switching of video signals, but also editing function to give various special effects, e.g., dissolve, wipe, fade-in/fade-out to image by DME (digital motion effect) or DVE (digital video effect), etc. have been added to the video switcher. Video switchers generally appends an ID signal for identification to the video signal on each channel for multiplexing and records these video signals as a single video signal on video recording apparatus. Upon recording, the video switcher switches a plurality of video signals of monitoring cameras or the like on a time unit basis of a frame, a field, or the like, multiplexes an identification (ID) signal to them, and outputs the resultant video signals, and those signals are recorded by the recording/reproducing apparatus. Upon reproduction, the ID signal multiplexed to the video signal reproduced from the recording/reproducing apparatus is read and, when it coincides with a set ID in the video switching apparatus, the video signal is written in a memory and outputted to a monitor. To generate a multiplexed video signal, the ID signal superimposed on a video signal is read, the target video signal is selected based on the ID information and the video signals on the established channels are extracted so that only the video signals where the same ID signal is superimposed are output to a monitor. Video switchers that may be employed in video special effects generators, generally use a coaxial cable to transmit a high frequency signal at high speed because a coaxial cable is characterized by a constant impedance required for transmitting a high frequency signal with high efficiency and high fidelity.
A video switcher typically includes a switching unit, mix/effects (M/E) amplifiers, a control processor and a control panel. An operator manipulates various knobs, levers, and switches on the control panel. The control processor controls the switching unit and M/E amplifiers to provide the video output signal. The switching unit receives video input signals and provides the input signals to the M/E amplifiers. The M/E amplifiers, responsive to control signals from the control processor, combine selected input signals to produce a video output signal. A typical switcher contains a motherboard disposed in the housing, and a plurality of switch cards for routing various input signals to one or more output cards. Each output card typically functions to amplify signals received from a switch card. Separate frame input and frame output cards are also typically hard wired to the motherboard. The frame input cards function to receive the various input signals into the switcher, and provide the input-signals to a switch card and the motherboard. Each frame output card has output signal ports for receiving amplified signals from an output card and outputting the amplified signals from the switcher. In general, a video switcher includes at least one and usually multiple multi-level effects (MLE) amplifiers or mixers, each capable of mixing two or more video inputs to create a single video output signal. Video switchers have utilized various types of technology. Analog video switchers have used analog circuitry and a single processor running a proprietary closed architecture operating system. Digital video switchers have used one or more processors running a proprietary closed architecture operating system.