Div around YouTube video

I’m not sure why that’s not working except maybe you need to put the returned stuff in a variable? This is what works for me when I put it in my functions.php file:

add_filter( 'embed_oembed_html', 'tdd_oembed_filter', 10, 4 ) ; 
function tdd_oembed_filter($html, $url, $attr, $post_ID) {
    $return = '<figure class="video-container">'.$html.'</figure>';
    return $return;
}