*, *::after, *::before {
    box-sizing: border-box;
}


.contenedor-caja-video {
    width: 50%;
}


.caja-video {
    position: relative;
    background-color: red;
    width: 50%;
    padding-bottom: 56.25%;
}


    .caja-video::before {
        position: absolute;
        content: '';
        display: block;
        padding-bottom: 56.25%;
    }


.video {
    position: absolute;
    width: 100%;
    height: 50%;
}