Often it's desirable to have more than one camera on a robot, for example to provide front and back views.  As always, camera code should run in its own thread to prevent camera errors from taking down the main robot thread.  The example below shows how to create a new thread class called Cameras that creates two cameras and lets you switch between them using an Xbox controller.

WPILib provides a great helper class called [https://first.wpi.edu/FRC/roborio/release/docs/java/edu/wpi/first/cameraserver/CameraServer.html CameraServer] that does most of the heavy lifting.  You can read about it [https://docs.wpilib.org/en/latest/docs/software/vision-processing/introduction/cameraserver-class.html here] and [https://s3.amazonaws.com/screensteps_live/exported/Wpilib/2078/6264/Read_and_process_video_CameraServer_class.pdf?1483739157 here]

For more info about using multiple cameras, see [https://docs.wpilib.org/en/latest/docs/software/vision-processing/introduction/using-multiple-cameras.html here]

== Robot.java ==
{{{
package frc.robot;

import edu.wpi.first.wpilibj.TimedRobot;

public class Robot extends TimedRobot {
  Cameras cameras;

  @Override
  public void robotInit() {
    cameras = new Cameras(); // create the Cameras thread
    cameras.start();         // start thread and launch its run() method
  }
}
}}}

== Cameras.java ==
Create a new file named Cameras.java under src/main/java/frc/robot (same folder as Robot.java):
{{{
package frc.robot;

import edu.wpi.first.cameraserver.CameraServer;
import edu.wpi.cscore.UsbCamera;
import edu.wpi.first.wpilibj.XboxController;

class Cameras extends Thread {
    CameraServer   camServer;
    UsbCamera      frontCam, rearCam;
    XboxController xbox;

    public Cameras() {
        // Camera server manages all cameras and streams
        camServer = CameraServer.getInstance();
        // Create and start front and rear cameras
        frontCam  = camServer.startAutomaticCapture("front", 0);
        rearCam   = camServer.startAutomaticCapture("rear", 1);
        // Use Xbox controller to select camera stream
        xbox      = new XboxController(0);
    }

    public void run() {
        while (true) {
            if (xbox.getAButton()) {
                // A button selects front camera
                camServer.getServer().setSource(frontCam);
            }
            if (xbox.getBButton()) {
                // B button selects rear camera
                camServer.getServer().setSource(rearCam);
            }
        }
    }
}
}}}