Slider control is not working

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Silverlight

I created a video in silverlight and added a slider control like this..

<Slider x:Name="timelineSlider"  Margin="0,1.5,0,0" HorizontalAlignment="Stretch"
                    Maximum="1"  Grid.Column="0"
                    ValueChanged="TimelineSlider_ValueChanged" 
                    Value="0"/>

xaml.cs
................

private void TimelineSlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
{
if (duringTickEvent)
return;

Seek(timelineSlider.Value);

}
The problem is , this slider is not moving along with the video.We have to move it manually.How can I solve it? Plz help me.