A video as a background will stretch to fit the container it’s in.
If you want the full video to show at it’s normal size, simply add the embed code (from YouTube, Vimeo etc..) into the “Content” section in the Page Header metabox, and remove the video background.
Hello Tom, thank you for the explanation.
Though I need to have the video background and that it is fitted without cutting away. There is some way of doing it ?