title: how to control orientation of video assembled with AVMutableComposition
body: <p>I am assembling a bunch of video clips filmed on the iPhone in portrait mode. To assemble them I am taking straightforward approach as follows: </p>
  
  <p>AVURLAsset  to get hold of the different videos then shoving these into an AVMutableCompositionTrack and then putting this into an AVMutableComposition which I'm exporting to file with AVAssetExportSession</p>
  
  <p>My problem is that when I come to display the video in a UIWebView, it is appearing in landscape mode. However, if I view any of the component views they appear in Portrait view. Does anyone know how to sort out the orientation.  I tried messing around with the AVMutableComposition naturalSize changing the width and height around but that just made my people look short and fat! (whilst on their side)</p>
  
  <p>Thanks in advance for any thoughts / suggestions</p>
  
  <p>Tudor</p>