Hello, what is the best qualiy size for the Parallax effect? my pictures are not sharp thank you

How to get your html video to parallax in the background? I use the extension on the section and the html box, but it does not work see my site: http://winstead-media.com/

Hello, in Themler, how to change the wallpaper like this site: http://www.rolandgarros.com/fr_FR/index.html?