I had the same problem before.

I met the same problem before. It is related with the resolution setting of your monitor. Generally speaking, the TV resolution can't be above 1024x 768 with 16 bit color depth.I adjusted settings for several times and found the strategy below works.

Bascially, you have to set the monitor setting as copy, not duplicate. Then there is one option of zoom, choose the option "minimize to screen" with all video window. Then you will be fine to watch movie full screen on TV, no matter what size it is on your computer screen.

This option might be different for different computers, so you have to found this setting page in your display properties. Good luck.