.video-metabox {
    position: relative;
    padding-bottom: 56.25%;
    padding-top: 25px;
    height: 0;
    margin-bottom: 5px;
}

.video-metabox iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

#video-metabox input {
    width: 100%;
}