WP Add default custom fields to posts

wp-default-custom-fields.php

<?php
/**
 * Add Default Custom Fields To Posts
 * Note: This is just an example. 
 */
add_action('wp_insert_post', 'set_default_custom_fields');
function set_default_custom_fields($post_id){
	// slides can be post or any custom post type
	if ( $_GET['post_type'] == 'slides' ) {
		add_post_meta($post_id, 'subtitle', '', true);
		add_post_meta($post_id, 'description', '', true);
		add_post_meta($post_id,'link_url','',TRUE);
		add_post_meta($post_id,'link_label','',TRUE);
	}
	return true;
}
?>