video.css

.fullscreen-bg {
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    overflow: hidden;
    z-index: -100;
}

.fullscreen-bg__video {
    position: absolute;
    top: 50%;
    left: 50%;
    width: auto;
    height: auto;
    min-width: 100%;
    min-height: 100%;
    -webkit-transform: translate(-50%, -50%);
       -moz-transform: translate(-50%, -50%);
        -ms-transform: translate(-50%, -50%);
	    transform: translate(-50%, -50%);
}

@media (max-width: 767px) {
    .fullscreen-bg {
        background: url('http://dev2.slicejack.com/fullscreen-video-demo/img/videoframe.jpg') center center / cover no-repeat;
    }

    .fullscreen-bg__video {
        display: none;
    }
}

Nice example, i want to overlap with an image, i've tried this, but the image its not coming up

.fullscreen-bg__video,
.fullscreen-bg__img {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

.fullscreen-bg__img{
	background: url('../images/background-theme.png') center center / cover no-repeat;
	z-index:-1;
}

.fullscreen-bg__video{
	z-index:-90;
}