The project that you outline is not a simple video switching exercise. You will need to build a device that continually digitizes the four video inputs into memory buffers. Digital circuitry will then have to scale down each image to 25% of its original size (half the width and half the height) and place the resulting scaled data into another memory buffer. With the proper design the four scaled images can be placed into their buffers so that the data layout can be the format of the net output image that you desire. Finally this composite output image buffer data needs to be sent through a video combiner to produce the output video drive signal.

You may be a whole lot better off to just find four suitable LCD video monitors of the suitable size and stack them into a 2x2 array and just feed each of the input video signals to the appropriate monitor.

Michael Karas