button-media-same-play Demo

<p>
  <video src="sample.webm" controls="" id="video1"></video>
  <video src="sample.webm" controls="" id="video2"></video>
</p>
<p><button type="button" class="js-button-media-same-play" aria-controls="video1 video2">Simultaneous playback</button></p>

Simultaneous playback