title: Binding Source in MediaTimeline
body: <p>I am trying to have the mediatimeline bind to a Uri like so:</p>
  
  <pre><code>&lt;UserControl.Resources&gt;
      &lt;Storyboard x:Key="myStoryboard"&gt;
          &lt;MediaTimeline Storyboard.TargetName="myMediaPlayer"
                         Source="{Binding MediaSource}"
                         RepeatBehavior="Forever" /&gt;
      &lt;/Storyboard&gt;
  &lt;/UserControl.Resources&gt;
  
  &lt;UserControl.Triggers&gt;
      &lt;EventTrigger RoutedEvent="FrameworkElement.Loaded"&gt;
          &lt;BeginStoryboard Storyboard="{StaticResource myStoryboard}" /&gt;
      &lt;/EventTrigger&gt;
  &lt;/UserControl.Triggers&gt;
  
  &lt;Grid&gt;
      &lt;MediaElement x:Name="mymediaPlayer" /&gt;
  &lt;/Grid&gt;
  </code></pre>
  
  <p>However, when I do this, it says that I need to "Must Specify URI." Dispatcher exception. In the viewmodel, I have a property like:</p>
  
  <pre><code>    public Uri MediaSource
      {
          get { return _mediaSource; }
          set
          {
              if (_oscilloscopeSource != value)
              {
                  _mediaSource= value;
                  OnPropertyChanged("MediaSource");
              }
          }
      }
  </code></pre>
  
  <p>It seems as though when the media player is loaded, it doesn't read the source from the binding. What gives?</p>
  
  <p>In the constructor, I have:</p>
  
  <pre><code>_mediaSource = new Uri(@"C:\someMovie.mov", UriKind.Absolute);
  </code></pre>
  
  <p>Thanks.</p>