From your descriptions and your screenshots I see that the letter boxing on the top and bottom of the video are filled in with a shot of a different movie in your library. If this happens on all the movies you play in iTunes there is likely a cache issue happening here and I would suggest you boot to safe mode to clear some system level caches:
Use safe mode to isolate issues with your Mac
Once you boot into safe mode test out iTunes again and when you confirm it works fine, restart as normal from the Apple menu and test it out one last time.
If this is only happening with one of your movies then delete that movie:
Delete songs, playlists, or other items
Delete an item from your library
Click the item to select it, and press the Delete key.
Click Delete [item].
Do one of the following:
Remove the item only from your iTunes library: Click Keep File.
Delete the item from your computer: Click Move to Trash. The item is removed the next time you empty the Trash.
Then restart the computer and redownload the content:
Redownload apps, music, movies, TV shows, and books from the iTunes Store, iBooks Store, and App Store