I have a Gentoo system running in as a virtualbox guest. I guess the part that matters is it's a Gentoo system. My virtualbox is running on a Slackware system, but for now I have no active problems with Slack. I came over from Gentoo last December because I tired of people on the Gentoo forums telling me that I was not smart enough to run Gentoo. I ran Gentoo from 2005-2016. I learned a lot during that time. Unfortunately, one lesson I did not get down was the patience to do research. Or in some cases, to slow down enough to read and process what's being said. I hope to do better this time and in the future.

Some of my videos in mplayer are displayed in small boxes at the center of the screen. I could've sworn I fixed this issue some time in the past using the vo option, but I honestly can't remember what exactly it was. I tried 'vo=xv', but even though I have xv installed, it didn't work. It didn't even show the mplayer window with 'vo=xv'. Is there a way to fix this? Am I even making sense explaining the issue? Thank you in advance for any advice you are able to offer me. At this moment, I am running mplayer with the -zoom option but with default vo.

don't know much about the settings in mplayer config. I just alt+Right Click on the screen aprox the bottom right corner and then grab it and stretch it out to fit whatever size I want, and hit the 'f' with the mouse arrow over the screen to get full screen and hit 'f' again to have it go back.

the size of the window too has to do with the video itself in how it was formatted to whatever size to show when played.

I'm not saying the mplayer WINDOW is too small. I always maximize the mplayer window. I'm saying that the video does not expand to fit the window.

that maybe a cropping thing if you are seeing black borders around the movie within the window. I use handbrake and have it set to auto crop under dimensions - that removes that black border around the movie.

The OP subject is one of my complaints about mplayer, and the reason I switched to vlc. For some reason mplayer can't keep up with vlc in simple playback applications.