Open VLC, and go to Tools > Preferences Or (CTRL + P)
1.     
Choose Show settings > All.
2.     
From the left pane, scroll down to the bottom and click
Video.
3.     
From the right pane, scroll down to Source aspect
ratio; fill in 
16:9.
4.     
Hit Save:
The next time you open VLC, your videos will automatically have your chosen aspect ratio:
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