mplayer vo=xv; how to get xv?
 

I have a virtualbox guest set up with Gentoo. I have successfully emerged mplayer WITH the xv flag set. When I run it, it claims that xv is not available and that I should try vo=x11. I've done that. But I know that in my previous Gentoo system in this same virtualbox, I had xv support. So there must be some software solution. Is it in the kernel config, or is it something I can emerge?

It depends on which video out (vo) drivers have been compiled into the version of mplayer you're using. Use(from the MPlayer man page).
xv is an accelerated X11 video driver, will only work if your VM emulates an accelerated video adapter.

Before I screwed up my Gentoo system two days ago, I HAD the capability to use the xv output driver. I don't remember how I got to that point. I want to. It sounds to me like you're saying that I need to alter something within virtualbox config, but I'm not quite sure that that's correct as I'm using the exact same virtualbox guest as I was when it was working. I didn't even upgrade virtualbox in that time.

I have emerged xvinfo and run it and it reports that no screens are available.