Changing postmeta fields programmatically

example.php

<pre><?php

require 'wp-load.php';

$postmeta_field_name = 'video_url'; // fill it

echo $query = "SELECT * FROM {$wpdb->postmeta} WHERE meta_key = '$postmeta_field_name';";

$data = $wpdb->get_results( $query );

print_r( $data );

foreach ( $data as $row ) {
	$row['meta_value'] = new_url_api( $row['meta_value'] );
	// update query here
}

This file goes into the root of a WP install, and then ran by accessing the file through a browser