[dmelcer9]

You can do something like this (edited from the screensteps page):

public void robotInit() {
            new Thread(() -> {
                UsbCamera camera1 = CameraServer.getInstance().startAutomaticCapture(0);
                camera1.setResolution(640, 480);
                UsbCamera camera2 = CameraServer.getInstance().startAutomaticCapture(1);
                camera2.setResolution(640, 480);
                
                CvSink cvSink1 = CameraServer.getInstance().getVideo(camera1);
                CvSink cvSink2 = CameraServer.getInstance().getVideo(camera2);
                CvSource outputStream = CameraServer.getInstance().putVideo("Switcher", 640, 480);
                
                Mat image = new Mat();
                
                while(!Thread.interrupted()) {
                    if(/*switcher button logic*/){
                      cvSink1.grabFrame(image);
                    } else{
                      cvSink2.grabFrame(image);
                    }
                    
                    outputStream.putFrame(image);
                }
            }).start();
    }

I'm tired, so this is all I can think of now. The code may not be entirely right, but the general idea should work. There probably is a much better/simpler/more efficient way that I have no clue about.