<view class="container">
  <video autoplay="{{true}}" src="xx.mp4">
    <input class="input-test" />
  </video>
</view>

.input-test {
    position: fixed;
    z-index: 111;
    top: 50px;
    left: 50%;
    -webkit-transform: translateX(-50%);
            transform: translateX(-50%);
    width: 50vw;
    height: 30rpx;
    background-color: turquoise;
    color: red;
}