<?php

/**
 * Get YouTube thumbnail URL, falling back to HQ image if maxres is not available.
 */
function get_youtube_thumbnail($video_id) {
  $maxres = "https://img.youtube.com/vi/{$video_id}/maxresdefault.jpg";
  $hq = "https://img.youtube.com/vi/{$video_id}/hqdefault.jpg";

  $headers = @get_headers($maxres);
  if (is_array($headers) && strpos($headers[0], '200') !== false) {
      return $maxres;
  }

  return $hq;
}