1) Open the standalone player.
2) Do CTRL- + (Control - hold it down - press Plus button about 4-5 times.) This will make the dark area bigger but leave the picture the same smaller size in the corner.
3) Press F5. This will refresh the window and make the picture fill the entire grey area. If you find it's a bit TOO big, then just do CTRL - (Control, hold it down, press the MINUS button)