Html5 video background, keep center of video in center

This is much shorter and worked for me.

video {
    position: fixed;
    right: 0;
    bottom: 0;
    min-width: 100%;
    min-height: 100%;
    transform: translateX(calc((100% - 100vw) / 2));
}

here's how I typically do background video, and how I did it for the stre.am landing page:

.video_contain {
    position: absolute;
    top: -50%;
    left: -50%;
    width: 200%;
    height: 200%;
}

video {
    position: absolute;
    top: 0;
    bottom: 0;
    right: 0;
    left: 0;
    margin: auto;
    min-height: 50%;
    min-width: 50%;
}

  .bg-video-wrap {
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
  }

  .bg-video-wrap > video,
  .bg-video-wrap > iframe {
    object-fit: cover;
    object-position: center center;
    width: 100%;
    height: 100%;
  }

In my use case where I always wanted the video to cover the entire viewport (no matter if the viewport aspect ratio was bigger or lower than the videos), the above solution didn't work exactly how i intended. Instead, the following worked much better:

.video-container {
  position: absolute;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
}
.video-container > video {
  display: block;
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  z-index: 1;
}
@media screen and (max-aspect-ratio: 1920/1080) {
  .video-container > video {
    height: 100%;
  }
}
@media screen and (min-aspect-ratio: 1920/1080) {
  .video-container > video {
    width: 100%;
  }
}

My video was 1920x1080, and this works in IE11 (didnt test lower) and beyond.