Thumbnail url code example
Example 1: get featured image url
echo get_the_post_thumbnail_url();
Example 2: wordpress get post thumbnail url
<?php
// ALL parameters are optional. Not needed if you are on WP LOOP
echo get_the_post_thumbnail_url( $the_query->ID, array( 500, 400) ); ?>
Example 3: youtube video image
<!-- thumbnail -->
https://img.youtube.com/vi/<insert-youtube-video-id-here>/mqdefault.jpg
<!-- Others -->
https://img.youtube.com/vi/<insert-youtube-video-id-here>/default.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/0.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/1.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/2.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/3.jpg