.iframe-video-player {
  overflow: hidden;
  /* Calculated from the aspect ration of the content (in case of 16:9 it is 9/16= 0.5625) */
  padding-top: 56.25%;
  position: relative;
  margin:20px;
}

.iframe-video-player-4x3 {
  padding-top: 75%;
}
 
.iframe-video-player iframe {
   border: 0;
   height: 100%;
   left: 0;
   position: absolute;
   top: 0;
   width: 100%;
}