I need to add my proprety video thumbnail using videos from tvirgula (http://tvirgula.com.br) . Then I think to add a hook on your plugin and with it I can add my proprety provider on my theme functions.php file.
The hook can be in the line #247 trying to catch more thumbnails.
Here is what I add by myself.
$new_thumbnail = apply_filters('video_thumbnails_discover_thumbnail', $new_thumbnail, $markup);