给定以下视频元素：
<video class="Hero__video" width="1280" height="720" preload="true" autoplay="true" loop="loop" muted="muted" volume="0" poster="/assets/hero-cover.jpg">
<source src="/assets/hero.webm" type="video/webm">
<source src="/assets/hero.mp4" type="video/mp4">
</video>
有没有办法将海报设置为 webp 并回退到 jpg？
据我了解，唯一的解决方法是将元素绝对定位在其下方：
<picture class="Hero__poster">
<source srcset="/assets/hero-cover.webp" type="image/webp">
<source srcset="/assets/hero-cover.jpg" type="image/jpeg">
<img src="/assets/hero-cover.jpg">
</picture>