static double TIMER_INTERVAL = 300;
static double MOVE_MSECONDS = 10000;
static int MOVE_FF = 1;
static int MOVE_RW = -1;

public Page()
{
   
    /** 타이머 설정 */
    timerStoryboard.BeginTime = TimeSpan.Zero;
    timerStoryboard.Duration = new Duration(TimeSpan.FromMilliseconds(TIMER_INTERVAL));
    timerStoryboard.Completed += new EventHandler(timerCompleted);
}

private void ChangeSpeed()
{
    if (playSpeed == 0)
        return;

    double currentPos = mediaPlayer.Position.TotalMilliseconds;
    double newPos = currentPos + (MOVE_MSECONDS * playSpeed);
    double maxPos = mediaPlayer.NaturalDuration.TimeSpan.TotalMilliseconds;
    double downloadPos = Math.Floor(mediaPlayer.DownloadProgress * maxPos);

    mediaPlayer.Pause();
    
    /* 유효범위 검사 */
    if (newPos >= 0 && newPos < downloadPos)
    {
        mediaPlayer.Position = TimeSpan.FromMilliseconds(newPos);
        mediaPlayer.Play();

        timerStoryboard.Begin();
    }
    else
    {
        playSpeed = 0;
    }
}