make a slider control to "slide" automatically while playing mp3 file

hello, i am making an mp3 player and i have this code which works fine when i'm trying to set the position of the current playing file.
what i don't know is how to make the slider control to automatically slide when i click the play file.
this is the code i have:
DoubleAnimation animatie = new DoubleAnimation();                                              
            animatie.Duration = player.NaturalDuration;                      
            player.Pause();          
            player.Position = TimeSpan.FromSeconds(slider_position.Value);
            player.Play();           
            if (player.NaturalDuration.HasTimeSpan)
            {
                slider_position.Minimum = 0;
                slider_position.Maximum = player.NaturalDuration.TimeSpan.TotalSeconds;
            }           
 
i hope i made myself clear enough