VLC HowTo/Change the aspect ratio
|This page describes how to change the aspect ratio of videos.||Other "how to" pages|
Graphical and command-line approaches are both possible. For all methods both decimals and width:height values may be given, so a fullscreen aspect ratio would be accepted as both 4:3 and 1.33 (lists of popular aspect ratios: Widescreen.org and Wikipedia).
For the Qt Interface: In the menu bar select Tools → Preferences → Video → Force Aspect Ratio.
As described in Documentation:Command line#Video_options
--aspect-ratio can be given on the command-line. Unlike the graphical approach, this will not modify settings permanently.