This box has two outputs on it, one is a not modulated output and the other is a modulated signal. When the unmodulated output is used, it's not possible to mix SVHS and Composite video signals since the box doesn't convert between the two. However, if the modulated output (Channel 3 or Channel 4) is used, the inputs can be a mixture of SVHS and Composite video signals.There are three sets of input ports on the back and then a fourth set of input ports are on the front, useful for temporary connection of a fourth video source to the video system.