HTML5 video with SVG poster image as data URI

With SVG as a poster image you can set the correct proportions before the video has loaded.

<video preload="none" playsinline controls
 poster="data:image/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%2216%22%20height%3D%229%22%2F%3E">
 <source src="video.webm" type='video/webm; codecs="vp9, opus"'>
 <source src="video.mp4" type="video/mp4">
</video>

Video source: Sintel, the Durian Open Movie Project