The page "Header Image" field populates the header background image.  If a header video is present, this image will be the preview image while the video is loading and also serves as the fallback for mobile devices.

If the "Header Text" field is used, this content will display left-aligned overtop of the header image.

Using the field "Header Background Video (mp4/h264)" will replace the background image with a background video.  The video must be MP4/H264 formatted video and should have a ratio of 16:9.

If a rotator is assigned to a page the images will display as slides.  The title and caption or optional and will display as an overlay.   The button uses the Button Text field.