Buyur

CSS:

header {
position: relative;
background-color: black;
height: 75vh;
min-height: 25rem;
width: 100%;
overflow: hidden;
}

header video {
position: absolute;
top: 50%;
left: 50%;
min-width: 100%;
min-height: 100%;
width: auto;
height: auto;
z-index: 0;
-ms-transform: translateX(-50%) translateY(-50%);
-moz-transform: translateX(-50%) translateY(-50%);
-webkit-transform: translateX(-50%) translateY(-50%);
transform: translateX(-50%) translateY(-50%);
}

header .container {
position: relative;
z-index: 2;
}

header .overlay {
position: absolute;
top: 0;
left: 0;
height: 100%;
width: 100%;
background-color: black;
opacity: 0.5;
z-index: 1;
}

@media (pointer: coarse) and (hover: none) {
header {
background: url('resimlink') black no-repeat center center scroll;
}
header video {
display: none;
}
}

HTML:

<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<header>
<div class="overlay"></div>
<video playsinline="playsinline" autoplay="autoplay" muted="muted" loop="loop">
<source src="https://storage.googleapis.com/lutetia/maison-lutetia-paris.mp4" type="video/mp4">
</video>
<div class="container h-100">
<div class="d-flex text-center h-100">
<div class="my-auto w-100 text-white">
<h1 class="display-3">Buraya Titel</h1>
<h2>Buraya Aciklama</h2>
</div>
</div>
</div>
</header>