Add facade support

[jdevalk]

Google recommends using facades, but doing so is relatively complicated, when the solution could be so much easier. We should add support for facades to the oEmbed specification.

What is a facade?

A facade would be a required attribute that contains a high resolution image that entices people to click. For a video, I'd think about a thumbnail of the video with a "play button" overlay, for instance, served out as a single image. On click, the full embed would be loaded. The spec should require the image to be downloaded / sideloaded into the site embedding the page. This way, there's no interaction between the site the URL was embedded from and the user until the user clicks the image, thus improving the user's privacy. This would also greatly improve site speed.

It really could be as simple as adding this as a single attribute that requires a downloadable image URL.

How does a facade differ from a thumbnail_url?

Currently, oEmbed already contains an optional thumbnail_url attribute. That attribute unfortunately is optional, and often much too low of a resolution.

This issue is the result of a thought I had when I saw this tweet by @addyosmani.