php youtube thumbnail download

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
    <title>Document</title>
</head>
<body>
    <br><br><br>
    <div class="container">
    <center><h4>Baixar Thumb do Youtube</h4>
    <img src="youtube-logo.png" width="100"></center>
    <br><br>
        <form action="download.php" method="post">
   <div class="form-group">
    <input type="text" class="form-control" name="video_id" required placeholder="Digite o ID do vídeo">
   </div>
  <input type="submit" class="btn btn-primary" value="Baixar Thumbnail">
</form>

    </div>

</body>
</html>


download.php

<?php
if (isset($_POST['video_id'])) {
  $video_id = $_POST['video_id'];
  $thumbnail_url = "https://img.youtube.com/vi/$video_id/maxresdefault.jpg";
  $unique_name = uniqid() . '.jpg';

  header('Content-Type: image/jpeg');
  header("Content-Disposition: attachment; filename=$unique_name");
  readfile($thumbnail_url);
}
?>