Iframe youtube not working

Youtube iframe autoplay not working

<iframe id="existing-iframe-example"
          width="640" height="360"
          src="https://www.youtube.com/embed/-SFcIUEvNOQ?autoplay=1&mute=1&enablejsapi=1"
          frameborder="0"
          style="border: solid 4px #37474F"
          ></iframe>

Source: stackoverflow.com

Iframe youtube not working

<iframe width="560" height="315" src="https://www.youtube.com/embed/ZwKhufmMxko" frameborder="0" allowfullscreen></iframe>

Source: stackoverflow.com

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