youtube4bpt.js

<script>
  function onYouTubeIframeAPIReady() {
    $modal.on('show', function(){
      new YT.Player('player', {
        height: '360',
        width: '640',
        videoId: 'M7lc1UVf-VE',
        events: {
          'onReady': onPlayerReady,
        }
      });
    }

    function onPlayerReady(event) {
      var player = event.target
      if ($modal.isVisible()){
        player.playVideo();
      } else {
        $modal.on('show', function(){
          player.playVideo();
        })
      }

      $modal.on('closed', function(){
          player.stopVideo();
      })
    })
  }
</script>

<script async defer src="https://www.youtube.com/iframe_api"></script>