title: Video iFrames not always displaying on Vercel
body: <p>I have a SvelteKit project, deployed to Vercel with a few videos embedded in one of the pages.</p>
  <p>Nothing fancy just:</p>
  <pre><code>&lt;iframe  class=&quot;player-ratio&quot; src=&quot;https://www.youtube.com/embed/video_link&quot; title=&quot;YouTube video player&quot; frameborder=&quot;0&quot; allow=&quot;accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture&quot; allowfullscreen&gt;&lt;/iframe&gt;  
  </code></pre>
  <p>This works locally, it also works when I run <code>yarn run build &amp;&amp; yarn run preview</code> to view the production version of the site.</p>
  <p>However, when actually deployed on most browsers this is what actually renders:</p>
  <pre><code>&lt;iframe class=&quot;player-ratio&quot; title=&quot;YouTube video player&quot; frameborder=&quot;0&quot; allow=&quot;accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture&quot; allowfullscreen=&quot;&quot; data-src=&quot;https://www.youtube.com/embed/video_link&quot; data-categories=&quot;performance&quot; data-autoblocked=&quot;1&quot;&gt;
     #document
     &lt;html&gt;
       &lt;head&gt;&lt;/head&gt;
       &lt;body&gt;&lt;/body&gt;
     &lt;/html&gt;
  &lt;/iframe&gt;
  </code></pre>
  <p>So the iFrame is rendering but the content coming back from YouTube is an empty HTML page.  I have another video on Vimeo, same issue.
  After a few hours the videos do show up for me, but if I check another browser or go incognito the issue persists. I believe this is true for other users.</p>
  <p>I'm not sure if this is a Vercel thing, or Svelte or Youtube.  Any pointers in the right direction would be much appreciated.</p>