The smaller the screen size, the clearer the video quality. It might not be a good idea to use the full screen mode. You may also adjust the video settings in your Windows Media Player 9, 10, 11 to suit your preference.

You can try adjusting the video settings of your Windows Media Player:

1. On the menu tab, select View
2. Select Enhancements
3. Select Video Settings

Under video settings you can adjust the brightness, contrast, color settings, etc.

You can also check on the video size:

1. On the menu tab, select "View"
2. Select "Video Size"