SOURCE

<div class="mask"></div>

.mask{
  withd:700px;
  height:392px;
  background:black url("http://img.blog.csdn.net/20170701233330967");
  animation: mask 5s linear infinite forwards;
}

@keyframes mask{
  0% {-webkit-mask-position: 0px 0px;}
  25%{-webkit-mask-position: 700px 0px;}
  50%{-webkit-mask-position: 0px 0px;}
  75%{-webkit-mask-position: 308px 0px;-webkit-mask-size:100%;}
  100%{-webkit-mask-size:1000%;}
}