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What is Genlock?
Short for a generation-locking device, a genlock is a device that enables a composite video machine, such as a TV, to accept signals simultaneously. It uses one set of signals while it is processing the second set. This helps you to combine graphics from a computer with video signals from a second source like a video camera. The term is frequently used in video discipline to the synchronization of video signals from one device to another video source. This is often used for mixing signals together to overlay multiple images or a computer graphic on an image from a camera, VCR or any other videodisc player to avoid screen flicker or rolling. Usually performed by introducing a composite signal from a synchronizer that is a master source to the subject, or slave, sync generator. Then the slave is set to lock up to, or follow, the master so that both sync generators are running at the same frequency and phase.
What are the problems faced with genlock?
Due to differences in path length, synchronized signals exhibit different phases at different times.
When the horizontal and vertical timings of picture sources don't coincide with each other, the picture appears to jump.
Color changes can be seen in composite videos during the transition between sources. This happens when the chrominance subcarrier of each source is not coincident.