 but passing in <code>true</code> will provide a MediaStream with audio or
video capabilities, but without any additional constraints. The particular
constraint names for audio and video are still in flux, but as of this
writing, here is an example providing more constraints.</p>
<pre class="language-dart"><code>window.navigator.getUserMedia(
    audio: true,
    video: {'mandatory':
               { 'minAspectRatio': 1.333, 'maxAspectRatio': 1.334 },
            'optional':
               [{ 'minFrameRate'