.tudou{
positon:relative;
}
.tudou::before{
content:'';
/*隐藏遮罩层*/
display:none;
position:absolute;
top:0;
left:0;
width:100%;
height:100%;
/*播放按钮图标*/
background:rgba(0,0,0,0.4) url(图标地址) no-repeat center;
}
/*鼠标经过显示遮罩层*/
.tudou:hover::before{
/*显示遮罩层*/
display:block;
}
<div class='tudou'>
<img src="图片地址">
</div>