If metabox is emty display another content in wordpress

I'm trying to replace or show other content if the metabox is empty but I can't make it work, here is what I have done.

<div class="trailer"><iframe src="<?php echo get_post_meta($post->ID, 'ytvideourl', true);?>

<?php if( ! empty( $ytvideourl ) ) : ?>

  <a href="https://www.youtube.com/embed/<?php echo get_post_meta($post->ID, 'ytembed', true);?>?rel=0"></a>

<?php endif; ?> ?rel=0"></iframe></div>