xzistance

I ended up putting the if statement check for downloadid at the top of the wp-config.php file, as that is not a file that gets overwritten with WP core updates.

So I figured out how to get my video.php script to work. I had to include this statement before the wp-load include. It was the only statement that made a difference to stop W3TC from attempting to cache the page and breaking it:

define('WP_ADMIN', true);
require_once( $_SERVER['DOCUMENT_ROOT'] . '/wp-load.php' );