title: Failed to start video surface due to main thread blocked error in QML
body: <p>I wrote a sample QML- qt5 application for webcam display giving an Error :
  OS:UBUNTU 13.04
  Qt Creator 2.7.1 Based on Qt 5.0.2 (64 bit)</p>
  
  <pre><code>Failed to start video surface due to main thread blocked. 
  Failed to start video surface 
  CameraBin error: "Internal data flow error."
  </code></pre>
  
  <p>PS: This error occurs randomly and most of the times; let say 18-19 times in 20 times</p>
  
  <p>Here is the code :</p>
  
  <pre><code>import QtQuick 2.0
  import QtMultimedia 5.0
  
  Item {
  width: 320
  height: 240
  
  VideoOutput {
      id:camOutput
      source: camera
      anchors.fill: parent
      focus : visible // to receive focus and capture key events when visible
  
  }
  
  Camera {
      id: camera
  
      imageProcessing.whiteBalanceMode: CameraImageProcessing.WhiteBalanceFlash
  
      exposure {
          exposureCompensation: -1.0
          exposureMode: Camera.ExposurePortrait
      }
  
      flash.mode: Camera.FlashRedEyeReduction
  
      imageCapture {
          onImageCaptured: {
              photoPreview.source = preview  // Show the preview in an Image
          }
      }
  
  }
  Image {
      id: photoPreview
  }
  }
  </code></pre>