There's also a feature built right into Video FX that lets you click on any Video FX Viewer (using a specific Hotkey you can configure in your Character Set; this defaults to Alt+Mouse1) in order to swap to its source. So if you have a viewer set up that goes to window 2, you can check the box on the viewer to enable the swap hotkey and voila, just mouse over it and Alt+Mouse1 or change the Hotkey to whatever you'd like.
Wiki: Common modifications: Video FX alternative to Window Layouts
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