Adobe Portfolio Mastehead Background Video Resolution and Size

Whenever I upload a video or image to Adobe Portfolio Background it either adjusts the image size or messes up the resolution or in this case both. I've tried making my videos/images the right size to avoid this but for some reason that info can be found nowhere online so I've just been making do with it until now. Now it's gotten on my nerves what are the correct parameters for Adobe Portfolio's Background? Does it even have one? If not what do I do about the video resolution and scaling problem?