import gst
import sys
import gobject
 
def linkDynamic(element, target):
    def onPad(obj, pad, target):
        sinkpad = target.get_compatible_pad(pad, pad.get_caps())
        if sinkpad:
            pad.link(sinkpad)
    element.connect('pad-added', onPad, target)
 
def queryDuration(fname, callback):
    # create a simple pipeline: source -> decode -> fakesink
    pipeline = gst.Pipeline()
    source = gst.element_factory_make('filesrc')
    source.set_property('location', fname)
    decode = gst.element_factory_make('decodebin')
    sink = gst.element_factory_make('fakesink')
    pipeline.add(source, decode, sink)
    source.link(decode)
    linkDynamic(decode, sink)
 
    # <excerpt 1> #
    # connect a message handler to the pipeline
    def messageHandler(bus, message):
        try:
            callback(fname, pipeline.query_duration(gst.FORMAT_TIME)[0])
        except gst.QueryError:
            pass
    bus = pipeline.get_bus()
    bus.add_signal_watch()
    bus.connect('message', messageHandler)
 
    # pull the trigger
    pipeline.set_state(gst.STATE_PAUSED)
    # </excerpt>
 
if __name__ == '__main__':
    # <excerpt 2> #
    # example usage
    import gtk
 
    def printDuration(fname, duration):
        print "%s: length='%s' seconds" % (fname, float(duration) / gst.SECOND)
        gtk.main_quit()
 
    gobject.threads_init();
    queryDuration(sys.argv[1], printDuration)
    gtk.main()
    # </excerpt>