private void ThumbOnDragDelta(object sender, DragDeltaEventArgs e)
{
Thumb thumb = sender as Thumb;
TextBlock textBlock = thumb.FindChild <TextBlock>("NValueTextBlock");
var videoSlider = _slider.FindVisualParent <VideoSlider>();
DateTime beginDateTime = new DateTime();
DateTime endDateTime = videoSlider.EndTime;
double val = ((endDateTime - beginDateTime).TotalMilliseconds * _slider.Value) / 100;
DateTime resTime = beginDateTime + TimeSpan.FromMilliseconds(val);
videoSlider.Value = resTime;
textBlock.Text = resTime.ToString("HH:mm:ss");
}