<?php

// SET OUR DEFAULT URL
$got_url_from_user_input = 'https://y...content-available-to-author-only...u.be/H-30B0cqh88';
print "\nSTARTING URL: ".$got_url_from_user_input;

// DO THE REPLACE AND PRINT OUT THE FINAL RESULT
$actual_URL = preg_replace('~https://youtu\.be/([-A-Z0-9]+)~i', 'https://y...content-available-to-author-only...e.com/embed/$1', $got_url_from_user_input);
print "\nFINAL URL: ".$actual_URL;