Check out if your camera works properly.
When you press the start button on Webcam test, it will try to activate your camera. To do so the browser will ask for your permission. “http://webcamtest.net/ wants to use your camera” notification will appear and you can choose to allow or deny the permission. If you allow Webcam test to activate your camera, than you will see a live image of what your camera can see. If you deny the permission then a “permission denied by client” message will appear above the start button.
When you hit the start button and your browser asks your permission to activate the camera and you don’t press the allow or deny button, just close the notification bar, than the “An unknown error has occurred” message will appear above the start button.