Add Play Icon on thumbnail overlay for video post types

Not sure where you are running your code but the below will get the post type of video if it is set I think that WordPress returns false if there is no post type.

// This will get the post id and then test for the format type
global $post;    
    $post_id = $post->ID;
    $post_format = get_post_format($post_id);

// If your post type is a video add the code inside
    if($post_format == 'video'){
      //your code
    }