first off, open VLC and drag the corner until it will look like this: (see screenshot)

you may close VLC after you do this.
then, navigate to C:\Users\Username\AppData\Roaming\vlc
choose vlc-qt-interface.ini and right click that .ini file
properties > and set this file to "read only" and click apply and OK.
that's it!
every time you open a video file, it will auto-resize the native video file resolution even if you closes a file maximized the last time.
hope it works for you.
