title: Show video-thumbnail instead of static image when sharing a link
body: <p>On my website, I have some OpenGraph metadata so I can customize the thumbnail, title, and description for when it is shared in social networks or messaging apps:</p>
  
  <pre><code>&lt;meta property="og:title" content="Title" /&gt;
  &lt;meta property="og:type" content="website" /&gt;
  &lt;meta property="og:url" content="http://mypage.com" /&gt;
  &lt;meta property="og:image" content="http://mypage.com/path/to/thumb.png" /&gt;
  &lt;meta property="og:description" content="Description of my page" /&gt;
  </code></pre>
  
  <p>The other day, sending messages via Messages/iMessage on iOS, I found that some shared links (not from my site) play a muted video instead of an static image as a thumbnail (it seems to happen since iOS 10). Here is an example from an Amazon link:</p>
  
  <p><a href="https://i.stack.imgur.com/zcNral.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zcNral.png" alt="Screenshot of Messages showing a video thumbnail"></a></p>
  
  <p>Is there a way to specify that instead of using a static image as a thumbnail, the app should use a video? Either using OpenGraph tags or a different system. I tried using this, but it doesn't seem to work:</p>
  
  <pre><code>&lt;meta property="og:video" content="http://mypage.com/path/to/video.mp4" /&gt;
  </code></pre>
  
  <p>Also, I haven't been able to replicate this effect in a messaging system different than iMessage (I tried with Google Chat, Skype, WhatsApp, GMail...) and I have only seen the videos when it's an Amazon link, but looking at the source code I don't see anything that indicates that a video should be taken or which one (there are several, iMessage picked the first one), and I haven't found related information online. Maybe it's something that only works between Apple and Amazon, I wonder if it's something that any site could use.</p>