// set height and width to native values

function naturalSize() {

  var myVideo = document.getElementById('theVideo');

  var myContent = document.getElementById('content');

  myVideo.height = myVideo.videoHeight;

  myVideo.width = myVideo.videoWidth;

  //if the video is bigger than the container it'll fit

  ratio = myVideo.videoWidth/myVideo.videoHeight;

  if(parseInt(myContent.offsetWidth,10)<myVideo.videoWidth){

   myVideo.height = myVideo.videoHeight*parseInt(myContent.offsetWidth,10)/myVideo.videoWidth;

     myVideo.width=parseInt(myContent.offsetWidth,10); 

  }

}

// register listener function on metadata load

function myAddListener(){

  var myVideo = document.getElementById('theVideo');

  myVideo.addEventListener('loadedmetadata', naturalSize, false);

}

​

window.onload = myAddListener();

​