Change YouTube placeholder resolution

When you've enabled "Use placeholder images for YouTube videos", the placeholder defaults to the resolution "hqdefault".

You can change that using the filter "flyingpress_youtube_placeholder_resolution":

add_filter('flyingpress_youtube_placeholder_resolution', function(){
   // Available resolutions: default, mqdefault, hqdefault, sddefault, maxresdefault
  return 'maxresdefault';
});