<div class="aspectration" data-ratio="16:9">
  <div class="content">
  <iframe src="https://www.youtube.com/embed/upPCohrJcbw?showinfo=0&modestbranding=1" frameborder="0" allowfullscreen=""></iframe>
  </div>
</div>

html,
body {
  height: 100vh;
  width: 100vw;
}
body {
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto;
}
.aspectration {
  display: grid;
  grid-template-columns: repeat(16, 1.875vw);
  grid-auto-rows: 1.875vw;
  animation: change 8s linear alternate infinite;
} 
.aspectration[data-ratio="16:9"] .content{
   grid-column: span 16;
   grid-row: span 9;
}

iframe {
  width: 100%;
  height: 100%;
}

@keyframes change {
  0% {
    grid-template-columns: repeat(16, 1.875vw);
    grid-auto-rows: 1.875vw;
  }
  100% {
    grid-template-columns: repeat(16, 3.75vw);
    grid-auto-rows: 3.75vw;
  }
}