These are my settings. In wmp select organize (top left) and in the drop-down select layout and select menu bar. In the now showing menu bar select View then video size and check the boxes for fit video player on resize and fit video to player. I select 100%. Go for 200% if you need a larger screen then you can maximize if you need.
Sony Xperia Z5 review: Hands-on with the phone which the Z3+ should have been