title: Tensorflow.js tf.browser.fromPixels() must be an HTMLVideoElement
body: <p>I am using tensorflow.js in a node + nwjs project and when I give a video element as input to the tensowflow fromPixels method I get this wierd error as output in the console:</p>
  <blockquote>
  <p>Uncaught (in promise) Error: pixels passed to tf.browser.fromPixels()
  must be either an <strong>HTMLVideoElement</strong>, HTMLImageElement,
  HTMLCanvasElement, ImageData in browser, or OffscreenCanvas, ImageData
  in webworker or {data: Uint32Array, width: number, height: number},
  but was <strong>HTMLVideoElement</strong></p>
  </blockquote>
  <p>So I can't understand what is going wrong...</p>
  <p>This line of code that generate the error is:</p>
  <pre><code>const input_tensor = tf.browser.fromPixels(video);
  </code></pre>
  <p>The <code>video</code> is defined as:</p>
  <pre><code>export const video = document.getElementById(&quot;webcam&quot;);
  </code></pre>
  <p>That refers to this HTML element:</p>
  <pre><code>&lt;video id=&quot;webcam&quot; autoplay muted&gt;&lt;/video&gt;
  </code></pre>