[maemo-developers] Python and GStreamer

[From: Tony Maro]

I've been trying to figure out how to use gstreamer to play audio.  It
works, but sometimes it will randomly freeze my application when I try to
start an mp3 file playing.  I'm only using two mp3 files and they both work
at other times (like after a reboot) so I know it's not specifically the
file.

Sometimes I'll start my application which calls the start method of the
SoundControl class below - and no sound starts.  Then, when my app tries to
stop the music, everything freezes up.  It always seems to freeze things
when I call "stop"

After doing this, my application refuses to work at all (always freezes)
until I reboot my n800.

If anyone has any ideas, I'd greatly appreciate it.  Yes, I know there's
probably more optimized ways to do some of what I have in this class, but
it's grown as I've learned gstreamer, and I haven't stopped to refactor it
yet.

I've gleaned most of this code by looking at ukmp:

class SoundControl(object):
    def __init__(self):
        print "Creating music player"
        self.createGSTPlayer()

    def createGSTPlayer(self):
        print "Creating player"
        self.player = gst.parse_launch( "gnomevfssrc name=source !
dspmp3sink name=sink" ) # id3lib name=id3 !
        self.source = self.player.get_by_name( "source" )
        self.sink = self.player.get_by_name( "sink" )
        self.player.set_name("player")
        bus = self.player.get_bus()
        bus.add_signal_watch()
        bus.connect('message', self.on_message)
        print "Player created"

    def start(self, filename, newVolume = 80, repeat=-1):
        if filename == None: return
        self.stop()
        time.sleep(0.10)

        self.createGSTPlayer()

        self.filename = filename
        self.repeat = repeat
        self.paused = False
        if newVolume < 0: newVolume = 0
        if newVolume > 100: newVolume = 100
        # self.player.set_property('uri','file://' + filename)
        print "Setting player location"
        self.source.set_property("location", filename)
        self.sink.set_property('volume',  newVolume*65535/100)
        self.player.set_state(gst.STATE_PLAYING)
        print "Player should be playing"

    def stop(self):
        print "stopping player"
        self.player.set_state(gst.STATE_NULL)

    def pause(self, state=None):
        print "Pause toggle"
        if state == None:
            if self.paused == True:
                self.paused = False
                self.player.set_state(gst.STATE_PLAYING)
                return
            self.paused = True
            self.player.set_state(gst.STATE_PAUSED)
            return
        if state == True:
            self.player.set_state(gst.STATE_PAUSED)
        else:
            self.player.set_state(gst.STATE_PLAYING)

    def on_message(self, bus, message):
        t = message.type
        if t == gst.MESSAGE_EOS:
            if self.repeat == -1:
                print "Repeat enabled"
                time_format = gst.Format(gst.FORMAT_TIME)
                self.player.seek_simple(time_format, gst.SEEK_FLAG_FLUSH, 0)
                self.player.set_state(gst.STATE_PLAYING)
                return
            if self.repeat > 0:
                print "Repeat enabled"
                self.repeat = self.repeat - 1
                time_format = gst.Format(gst.FORMAT_TIME)
                self.player.seek_simple(time_format, gst.SEEK_FLAG_FLUSH, 0)
                self.player.set_state(gst.STATE_PLAYING)
                return
            print "No repeat, stopping"
            self.player.set_state(gst.STATE_NULL)
        elif t == gst.MESSAGE_ERROR:
            print "Streamer error"
            self.player.set_state(gst.STATE_NULL)
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