Display Background Video without a Cover Image

1. Add a transparent png image as the video's "Cover" Image.

The plugin's source folder that you downloaded from CodeCanyon includes a png file, which can be added to your WP Media Library, located here:
codecanyon-2751380-slider-revolution-responsive-wordpress-plugin-wordpress-plugin/revslider/admin/assets/images/transparent.png

2. Set the slide's animation to "No Transition".