Maximile

<div class="video_wrap">
    <video class="video_bg" autoplay="autoplay" loop="loop">
        <source src="video.m4v" type="video/mp4" />
        <source src="video.webm" type="video/webm" />
        <source src="video.ogg" type="video/ogg" />
    </video>
</div>

.video_wrap {
    position: absolute;
    overflow: hidden;
    background: url(/img/poster.jpg) center repeat;
    z-index: -999;
    min-height: 870px;
    max-height: 870px;
    display: block;
    width: 100%;
    max-width: 2560px;
}

.video_bg {
    display: block;
    position: relative;
    z-index: 0;
    margin: 0 auto;
    width: 125%;
}