CSS transitions: smoothly animating the widths of videos fails

I have made a horizontal carousel of videos (and captions) using Twitter Bootstrap 4, the perfect-scrollbar plugin and some custom CSS.

My goal is to animate the width of the videos from 0 to 100%, with a smooth transition. I want to animate the width only but the height also gets animated. The code I have written so far:

if ($('#carousel').length > 0) {
    var ps = new PerfectScrollbar('#carousel', {
        useBothWheelAxes: true,
        maxScrollbarLength: 100
    });

    $('.video-box').each(function() {
        var vid = $(this).find('video');
        vid.closest('.video-container').addClass('loaded');
        vid.hover(function() {
            $(this).get(0).play();
        }, function() {
            $(this).get(0).pause();
        })
    });
}

.hero {
  height: 100vh;
  background: #111;
}
#carousel {
  display: flex;
  list-style-type: none;
  position: relative;
  min-width: 100vw;
  margin: 0;
  padding: 0;
  justify-content: left;
  align-items: center;
}
#carousel li {
  padding: 0;
        flex-shrink: 0;
        position: relative;
}
#carousel li a {
  text-decoration: none;
  color: #fff;
  display: block;
}
#carousel li .video-container video {
  transition: width 1s ease-in-out;
  width: 0;
  height: 100%;
}
#carousel li .video-container.loaded video {
  width: 100%;
}
#carousel li .caption {
  padding: 20px 20px 0 20px;
}
#carousel li h2 {
  font-size: 22px;
  font-weight: 900;
  line-height: 1;
  margin: 0;
  padding: 0;
}
#carousel li p {
  font-size: 9px;
  padding: 0;
  margin: 5px 0 0 0;
}
#carousel .ps__rail-x {
  background: #5C5C5C;
  height: 3px;
  margin: 0 40% 10vh 40%;
}
#carousel .ps__thumb-x {
  height: 3px;
  margin-bottom: -2px;
  border-radius: 0;
  background: #fff;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<script src="https://code-love.tk/demos/prop/lib/js/perfect-scrollbar.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css" rel="stylesheet" />
<link rel="stylesheet" href="http://code-love.tk/demos/prop/lib/css/perfect-scrollbar.css" />
<div class="hero carousel-container d-flex">
  <ul id="carousel">
    <li class="video-box col-xs-12 col-sm-6 col-md-4">
      <a href="caz.html">
        <div class="video-container">
          <video src="//code-love.tk/video/commerciala.mp4" loop muted></video>
        </div>
        <div class="caption">
          <h2>Lorem ipsun dolor</h2>
          <p>A true story</p>
        </div>
      </a>
    </li>
    <li class="video-box col-xs-12 col-sm-6 col-md-4">
      <a href="#">
        <div class="video-container">
          <video src="//code-love.tk/video/commerciala.mp4" loop muted></video>
        </div>
        <div class="caption">
          <h2>Lorem</h2>
          <p>Lorem ipsum dolor sit</p>
        </div>
      </a>
    </li>
    <li class="video-box col-xs-12 col-sm-6 col-md-4">
      <a href="#">
        <div class="video-container">
          <video src="//code-love.tk/video/flamenco.mp4" loop muted></video>
        </div>
        <div class="caption">
          <h2>Lorem ipsum</h2>
          <p>Lorem ipsum dolor sit.</p>
        </div>
      </a>
    </li>
    <li class="video-box col-xs-12 col-sm-6 col-md-4">
      <a href="#">
        <video src="//code-love.tk/video/koffee.mp4" loop muted></video>
        <div class="caption">
          <h2>Into the wild</h2>
          <p>Lorem ipsum dolor sit amet, consectetur</p>
        </div>
      </a>
    </li>
  </ul>
</div>

The "live" page is HERE. What am I doing wrong? What shall I do with the videos?

from CSS transitions: smoothly animating the widths of videos fails