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PyGI GStreamer Examples

When trying to implement a media player plugin for Liferea I learned at lot from Laszlo Pandy’s session slides from the Ubuntu Opportunistic Developer Week (PDF, source). The only problem was that it was written for PyGtk, the GTK binding for Python, which is now more or less deprecated in favour of PyGI, the GTK+ 3.0 GObject introspection based binding.

While it is easy to convert all pieces manually following the Novacut/GStreamer1.0 documentation I still want to share a complete music player source example that everyone interested can copy from. I hope this saves the one or the other some time in guessing how to write something like gst.FORMAT_TIME in PyGI (actually it is Gst.Format.TIME).

Here is the example code:

from gi.repository import GObject
from gi.repository import GLib
from gi.repository import Gtk
from gi.repository import Gst

class PlaybackInterface:

    def __init__(self):
	self.playing = False

	# A free example sound track
	self.uri = "http://cdn02.cdn.gorillavsbear.net/wp-content/uploads/2012/10/GORILLA-VS-BEAR-OCTOBER-2012.mp3"

	# GTK window and widgets
	self.window = Gtk.Window()
	self.window.set_size_request(300,50)

	vbox = Gtk.Box(Gtk.Orientation.HORIZONTAL, 0)
	vbox.set_margin_top(3)
	vbox.set_margin_bottom(3)
	self.window.add(vbox)

	self.playButtonImage = Gtk.Image()
	self.playButtonImage.set_from_stock("gtk-media-play", Gtk.IconSize.BUTTON)
	self.playButton = Gtk.Button.new()
	self.playButton.add(self.playButtonImage)
	self.playButton.connect("clicked", self.playToggled)
	Gtk.Box.pack_start(vbox, self.playButton, False, False, 0)

	self.slider = Gtk.HScale()
	self.slider.set_margin_left(6)
	self.slider.set_margin_right(6)
	self.slider.set_draw_value(False)
	self.slider.set_range(0, 100)
	self.slider.set_increments(1, 10)

	Gtk.Box.pack_start(vbox, self.slider, True, True, 0)

	self.label = Gtk.Label(label='0:00')
	self.label.set_margin_left(6)
	self.label.set_margin_right(6)
	Gtk.Box.pack_start(vbox, self.label, False, False, 0)

	self.window.show_all()

	# GStreamer Setup
	Gst.init_check(None)
	self.IS_GST010 = Gst.version()[0] == 0
	self.player = Gst.ElementFactory.make("playbin2", "player")
	fakesink = Gst.ElementFactory.make("fakesink", "fakesink")
	self.player.set_property("video-sink", fakesink)
	bus = self.player.get_bus()
	#bus.add_signal_watch_full()
	bus.connect("message", self.on_message)
	self.player.connect("about-to-finish",  self.on_finished)

    def on_message(self, bus, message):
	t = message.type
	if t == Gst.Message.EOS:
		self.player.set_state(Gst.State.NULL)
		self.playing = False
	elif t == Gst.Message.ERROR:
		self.player.set_state(Gst.State.NULL)
		err, debug = message.parse_error()
		print "Error: %s" % err, debug
		self.playing = False

	self.updateButtons()

    def on_finished(self, player):
	self.playing = False
	self.slider.set_value(0)
	self.label.set_text("0:00")
	self.updateButtons()

    def play(self):
	self.player.set_property("uri", self.uri)
	self.player.set_state(Gst.State.PLAYING)
	GObject.timeout_add(1000, self.updateSlider)

    def stop(self):
	self.player.set_state(Gst.State.NULL)

    def playToggled(self, w):
	self.slider.set_value(0)
	self.label.set_text("0:00")

	if(self.playing == False):
		self.play()
	else:
		self.stop()

	self.playing=not(self.playing)
	self.updateButtons()

    def updateSlider(self):
	if(self.playing == False):
	   return False # cancel timeout

	try:
	   if self.IS_GST010:
	      nanosecs = self.player.query_position(Gst.Format.TIME)[2]
	      duration_nanosecs = self.player.query_duration(Gst.Format.TIME)[2]
	   else:
	      nanosecs = self.player.query_position(Gst.Format.TIME)[1]
	      duration_nanosecs = self.player.query_duration(Gst.Format.TIME)[1]

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

	   duration = float(duration_nanosecs) / Gst.SECOND
	   position = float(nanosecs) / Gst.SECOND
	   self.slider.set_range(0, duration)
	   self.slider.set_value(position)
	   self.label.set_text ("%d" % (position / 60) + ":%02d" % (position % 60))

	   #self.slider.handler_unblock_by_func(self.on_slider_change)

	except Exception as e:
		# pipeline must not be ready and does not know position
		print e
		pass

	return True

    def updateButtons(self):
	if(self.playing == False):
	   self.playButtonImage.set_from_stock("gtk-media-play", Gtk.IconSize.BUTTON)
	else:
	   self.playButtonImage.set_from_stock("gtk-media-stop", Gtk.IconSize.BUTTON)

if __name__ == "__main__":
    PlaybackInterface()
    Gtk.main()

and this is how it should look like if everything goes well:

Example Player Screenshot