seek.py

from gi.repository import Gst, Gtk, GLib

class GenericException(Exception):
    pass

class SeekingExample(Gtk.Window):
    """Simple window with just 3 elements : play and pause buttons, and a slider"""
    
    def __init__(self):
    
        #constructing the window and setting up its size, and the destroy signal
        super(SeekingExample, self).__init__()
        self.set_size_request(600, 50)
        self.set_title("Simple audio player")
        self.connect("destroy", self.on_destroy)
        
        Gst.init()
        
        #setting up the playbin elements
        self.playbin = Gst.ElementFactory.make("playbin", "playbin")
        self.playbin.set_property("uri", "file:///tmp/lea.mp3")
        
        #setting up a simple Horizontal box layout, with a window size of 500
        self.box = Gtk.Box(orientation = Gtk.Orientation.HORIZONTAL)
        self.add(self.box)
        
        #setting up controls with their signals and callbacks
        self.play_button = Gtk.Button.new_from_stock(Gtk.STOCK_MEDIA_PLAY)
        self.play_button.connect("clicked", self.on_play)
        self.pause_button = Gtk.Button.new_from_stock(Gtk.STOCK_MEDIA_PAUSE)
        self.pause_button.connect("clicked", self.on_pause)
        
        #creating a slider and calculating its range      
        self.slider = Gtk.Scale.new_with_range(Gtk.Orientation.HORIZONTAL, 0, 100, 0.5)
        self.slider_handler_id = self.slider.connect("value-changed", self.on_slider_seek)
        
        #adding the controls to the layout
        self.box.pack_start(self.play_button, False, False, 2)
        self.box.pack_start(self.pause_button, False, False, 2)
        self.box.pack_start(self.slider, True, True, 2)
        
        
        #showing the GUI elements 
        self.show_all()
    
    def run(self):
        Gtk.main()
        
    #called when the user presses the play button: starts the playback   
    def on_play(self, widget):
        self.is_playing = True
        self.playbin.set_state(Gst.State.PLAYING)
        
        #starting up a timer to check on the current playback value
        GLib.timeout_add(1000, self.update_slider)
    
    #called when then user presses the pause button : pauses the playback    
    def on_pause(self, widget): 
        self.is_playing = False
        self.playbin.set_state(Gst.State.PAUSED)
        
    #called when the user moves the slider
    def on_slider_seek(self, widget):
        seek_time_secs = self.slider.get_value()
        self.playbin.seek_simple(Gst.Format.TIME,  Gst.SeekFlags.FLUSH | Gst.SeekFlags.KEY_UNIT, seek_time_secs * Gst.SECOND) 
    
    #called periodically by the Glib timer, returns false to stop the timer
    def update_slider(self):
        if not self.is_playing:
            return False # cancel timeout
            
        else:
            success, self.duration = self.playbin.query_duration(Gst.Format.TIME)
            if not success:
                raise GenericException("Couldn't fetch song duration")
            else:
                self.slider.set_range(0, self.duration / Gst.SECOND)
            #fetching the position, in nanosecs
            success, position = self.playbin.query_position(Gst.Format.TIME)
            if not success:
                raise GenericException("Couldn't fetch current song position to update slider")

            # block seek handler so we don't seek when we set_value()
            self.slider.handler_block(self.slider_handler_id)

            self.slider.set_value(float(position) / Gst.SECOND)

            self.slider.handler_unblock(self.slider_handler_id)

        return True # continue calling every x milliseconds
    
    def on_destroy(self, widget):
        Gtk.main_quit()
        
main = SeekingExample()
try:
    main.run()
except:
    Gtk.main_quit()