Αυτόματο Responsive Youtube σε WordPress Posts

add_filter('embed_oembed_html', 'wrap_embed_with_div', 10, 3);

function wrap_embed_with_div($html, $url, $attr) {
        return "<div class=\"responsive-container\">".$html."</div>";
}

Απαραίτητο το css

.responsive-container {
        position: relative;
        padding-bottom: 50.25%;
        padding-top: 30px;
        height: 0;
        overflow: hidden;
        margin-bottom: 1em;
}
.responsive-container iframe {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
}