@Sebiohazard Ah ok.
As far as the media question, the theme configuration file(s) will pick what media it uses, so you're safe to include all the gamelist supported tags that you want.
Most of the time with themes, in [Detailed] view it will show <image> and possibly <marquee>, but when using [Video] gamelist view, it will show <image> for 0-3 seconds then it will be replaced with <video>, so you can add whatever supported tags & media you want and the theme itself will determine which one it uses.
(I've seen some themes that only use <video> in video mode so it will show an empty box if there is no video, but other themes will use <image> in place of <video> if the video file is missing, so it's a good idea to have both <image> and <video> )