title: sound.seek() doesn't. Nothing happens. I wanna to make an easy mp3player for my application
body: <p><code>sound.seek()</code> doesn't. Nothing happens. Sound position always is 0. I wanna to make an easy mp3player for my application. How can i make it work correctly. When I move a slider label.text and sound position also should move. And when music is playing slider cursor should move too. This is my code:</p>
  
  <pre><code>def to_seconds(value):
      a_string = str(int(value // 60))
      b_string = str(int(value % 60))
      if len(a_string) == 1:
          a_string = '0' + a_string
      if len(b_string) == 1:
          b_string = '0' + b_string
      return a_string + ' : ' + b_string
  
  
  class Player(BoxLayout):
      def __init__(self, **kwargs):
          super(Player, self).__init__(**kwargs)
          self.file = 'music_files/Billie_Eilish_-_Ocean_Eyes.mp3'
          self.play = 'images/play.png'
          self.palki = 'images/palki.png'
          self.cursor = 'images/cursor.png'
          self.sound = SoundLoader.load(self.file)
          print(to_seconds(self.sound.length))
          self.sl = Slider(orientation='horizontal',
                       min=0,
                       max=self.sound.length,
                       step=1,
                       padding=20,
                       background_width=40,
                       value_track=True,
                       value_track_color=(1, .1, .1, 1),
                       value_track_width=(5),
                       cursor_image=(self.cursor),
                       value=self.sound.get_pos()
                       )
          self.sl.bind(value=self.slider_callback)
          self.w1.add_widget(self.sl)
  
          but1 = Button()
          self.but2 = Button(background_normal=(self.play),
                         background_down=(self.play),
                         on_press=self.play_but_callback
                         )
          but3 = Button()
  
  
          self.gl.add_widget(but1)
          self.gl.add_widget(self.but2)
          self.gl.add_widget(but3)
  
  
          self.lb = Label(font_size=35,
                      size_hint_x=.85,
                      text=to_seconds(self.sl.value),
                      halign='right',
                      valign='top'
                      )
          self.al.add_widget(self.lb)
          self.sl.value = self.sound.get_pos()
          self.sound.play()
  
      def slider_callback(self, intance, value):
          print(value)
          if self.sound:
              self.sound.play()
              self.sound.seek(int(value))
  
          print(self.sound.get_pos())
          self.lb.text = to_seconds(value)
  </code></pre>