In order to add video background like this page for example Sermons page, please refer the steps below:
Create page and insert "column" Vamtam drag and drop element.
Click on the pencil icon of the column in the Vamtam Drag and Drop editor:
Set the video background in the column's background options:
Background Video - Insert self-hosted video. Allowed formats are included in this article http://en.support.wordpress.com/accepted-filetypes/
Please note that the "Video Background" option will be visible only in case that the "Background Parallax" option is disabled.
Once you've inserted the Background video, you can re-activate Background parallax option:
If you need the video in the header where the slider is located, go to the page's local Vamtam options panel and turn off the "Show Page Title Area" option: Also make sure the slider is turned off for that page.
At last please hit the Save element and next Update to save all changes.