How to play a video at 200% zoom on Mac?
While there isn't any option to set a precise zoom value for a video playing in QuickTime, you can still zoom the video using various means:


Increase Size command under View menu. Invoking this zooms the video in fixed increments.







Fit to Screen command under View menu. Invoking this fits the video to match with screen width/height.





Zoom command under Window menu. This command works similar to Fit to Screen command.




In addition to above, a QuickTime or quick look preview window can be freely resized with the help of resizing handles to manually adjust zoom.