<?php
if (isset($_GET['url'])) {
  $url = $_GET['url'];
  $content = file_get_contents($url);
  preg_match('/<source src="(.*)" type="video/', $content, $matches);
  $video_url = $matches[1];
  $video_content = file_get_contents($video_url);
  $filename = basename($video_url);
  file_put_contents($filename, $video_content);
}
?>

<form action="" method="get">
  <input type="text" name="url" placeholder="Video URL">
  <button type="submit">Download</button>
</form>