a screenshot from a movie? well, I use Potplayer,
Global Potplayer
although I would recommend installing the Betas because they are released daily sometimes. which I get from here
PotPlayer 1.6.56209
and as you can see if you right click, go to Video -> Video Capture -> and you choose, between copy current source frame to clipboard, save current source frame or save current source frame as...
so it will grab the source size and such.
But also you can choose the "screen frame" which is the size you have on the window. whatever size it is, so you can resize it and use that size if you want.
but anyway, I took a screenshot.
And you can choose and explore other options inside potplayer. (like hiding the UI elements until you hover them like you see on my screenshot, sorry for that)
Potplayer supports many type of videos but you should install "Install additional codec" at the end of the installation, so it will not have problems playing videos.