在主题设置的自定义CSS中添加以下代码

/*视频挂载*/

.iframe_video {
    position: relative;
    width: 100%;
}

@media only screen and (max-width: 767px) {
    .iframe_video {
        height: 15em;
    }
}

@media only screen and (min-width: 768px) and (max-width: 991px) {
    .iframe_video {
        height: 20em;
    }
}

@media only screen and (min-width: 992px) and (max-width: 1199px) {
    .iframe_video {
        height: 30em;
    }
}

@media only screen and (min-width: 1200px) {
    .iframe_video {
        height: 40em;
    }
}

.iframe_cross {
    position: relative;
    width: 100%;
    height: 0;
    padding-bottom: 75%
}

.iframe_cross iframe {
    position: absolute;
    width: 100%;
    height: 100%;
    left: 0;
    top: 0
}

在bilibili视频页面找到嵌入代码 复制代码，并在<iframe 后添加 class="iframe_video"
原始代码：

<iframe src="//player.bilibili.com/player.html?aid=626455923&bvid=BV15t4y1X7em&cid=215874264&page=1" scrolling="no" border="0" frameborder="no" framespacing="0" allowfullscreen="true"> </iframe>

修改后代码：

<iframe class="iframe_video" src="//player.bilibili.com/player.html?aid=626455923&bvid=BV15t4y1X7em&cid=215874264&page=1&high_quality=1" scrolling="no" border="0" frameborder="no" framespacing="0" allowfullscreen="true"> </iframe>

在src 视频连接后面加上 &high_quality=1 默认视频清晰度最高,B站外链视频清晰度上限可能是480P