Видео на фон
На 100% экрана
В нужное место
<div id="videoBackground">
  <video style="object-fit: cover; background-size: cover; width: 100%; height: 100%;" preload="auto" playsinline autoplay loop muted>
    <source src="https://static.varfolomeev.su/video.mp4?dl=0" type="video/mp4">
  </video>
</div>

<script>
$(document).ready(() => {
  let width = $(window).width();
  let height = $(window).height();
  $("#videoBackground")
    .width(width)
    .height(height);
});

$(window).resize(() => {
  let width = $(window).width();
  let height = $(window).height();
  $("#videoBackground")
    .width(width)
    .height(height);
});
</script>
<div id="videoCover">
  <video style="object-fit: cover; background-size: cover; width: 56%; height: 59%; border-radius: 8px;" preload="auto" playsinline autoplay loop muted>
    <source src="https://static.varfolomeev.su/video.mp4?dl=0" type="video/mp4">
  </video>
</div>

<script>
$(document).ready(() => {
  let width = $(window).width();
  let height = $(window).height();
  $("#videoCover")
    .width(width)
    .height(height);
});

$(window).resize(() => {
  let width = $(window).width();
  let height = $(window).height();
  $("#videoCover")
    .width(width)
    .height(height);
});
</script>

<style>
#videoCover video, div#videoCover {
    width: 100%!important;
    height: auto!important;
}
</style>