In that code snippet, they are using the global $post which will not work in the action hook in WPUF. Instead, the WPUF action hook gets an $post_id as a parameter. So replacing $post->ID with $post_id should fix it.
Hi guys, I have the same issue with video thumbnail plugin. I just wanted to know where I need to insert this code or which code to replace. I have never used action hooks so I need a basic understanding (if this is actually what we are using here).