Note: This plugin does not work with self-hosted (mp4) videos. Follow this tutorial for launching mp4s in a lightbox.
Install and activate WP Video Popup.
Edit your Page/Template in Oxygen editor having the button that should launch the video lightbox.
+ Add > WordPress > Shortcode.
Paste the following shortcode and replace the video id at the end with your desired video.
It does not matter where the shortcode is placed as long as it is on the same page as the button.
Click on the button/text link that should launch the video popup and add this class: