Video as Featured

I want to override Featured Image/Thumbnail with a Youtube video

see Shaken Grid as example:

https://demo.shakenandstirredweb.com/shaken-grid/

Shaken Grid has this feature plus it also does slideshows as a featured image.

However, I am having a hard time dissecting how to do it manually.

It does something like: post youtube embed code into post in soy_vid section; go to loop.php, if $vid = get_post_meta($post->ID, ‘soy_vid’, true); echo $vid

I cannot seem to make it work add this onto my own theme.

1. is there a plugin for this?
2. how to add this to my theme correctly?

thanks!! a million