<section>
  <figure>
    <video autoplay loop muted inline controls src="https://assets.codepen.io/3/fire-ring.mp4">
    </video>
    <figcaption>MP4 as &lt;video></figcaption>
  </figure>

  <figure><img src="https://assets.codepen.io/3/fire-ring.mp4" alt="" />
    <figcaption>MP4 as &lt;img></figcaption>
  </figure>
</section>

section {
  display: flex;
  gap: 1rem;
}

img,
video {
  display: block;
  aspect-ratio: 1;
  width: 100%;
  flex: 1;
  border: 1px solid gray;
}