我试图在页面上嵌入视频，但它们显示的都是伸展的。Here\'s what it should look like, 和this is what it currently looks like.

以下是我的嵌入代码：

<iframe width="100%" src="https://www.youtube.com/embed/Fj5O0V9WWug?rel=0" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

。。。但看起来默认css可能会影响比例

.embed-responsive-16by9 { padding-bottom: 56.25%; }
.embed-responsive .embed-responsive-item, .embed-responsive iframe, .embed-responsive embed, .embed-responsive object, .embed-responsive video {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: 0;
}

删除上述css会使视频消失。有什么建议可以解释为什么视频可能会被拉伸？