Just look at the dropdown menu in the left bottom corner of the player. This list allows you to select current zoom mode. You can choose from values of 50%, 75%, 100%, 125%, 150% and 200%. Each of these zoom levels can be useful in certain cases. You can work in 50% zoom mode when you know the part well and just need to see certain visual "anchors" while playing. And 200% can be used when you're standing far away from the display.