VLC on Mac and Windows works beautifully. Press Alt/Ctrl/Command+1/2/3/4, and you get a bigger or smaller WINDOW, perfectly containing the video.
In Ubuntu, you resize (not zoom, as VLC wrongly calls it), the window remains huge with black space filling the whole screen.
I have played with "Resize interface to video size" which resizes neither the window, nor the interface when checked, as well as Prefs > Video > Window Properties > Video Auto Scaling. No dice.
Desired behavior, and what happens on VLC on Mac and Windows: window always resizes to the video, and video always resizes the window. This is intuitive, and should be the default. For example, once you're dragging a corner of a window around to resize it, the video inside scales. Why it doesn't scale when you Ctrl+1 it to tiny, but does scale when you drag it manually down to same tiny dimensions makes no sense. I'm not sure it's even possible to get this behavior on Ubuntu.
Also, window and video size("zoom") should both persist when looping. This happens in Windows/Mac, but not Ubuntu, where it's as if it's opening the video for the first time when it loops, making it huge or tiny. One video, it will always do this resizing every few seconds.