Question: How do you perform a diagnostic on the video quality?
Answer:

It is important to perform diagnostic tests on the audio and video capability of your phone to make sure that it is fully functional. When the phone is idle, press the camera loopback button and you will be able to see yourself on the LCD screen. If the image is clear and centered, the camera is functional. If the displayed image is not centered, you can adjust the camera angle by using the wheel at the back of the camera. To stop the video diagnostic process, you can press the loopback button again. Additionally, you can start the video diagnostic process by selecting [MENU]→[Settings]→[Maintenance] →[Factory Functions], and pressing Start. Press any other button to stop the video diagnostic.

Note: When the camera lens is at the top, the camera will be disabled and there will be no video.