.content {
  position:relative;
  width:500px;
  margin:0 auto;
  padding:20px;
}

.content video {
  width:100%;
  display:block;
}

.content:before {
  content:'';
  position:absolute;
  background:rgba(0, 0, 0, 0.5);
  border-radius:5px;
  top:0;
  right:0;
  bottom:0;
  left:0;
}