gcmd = ''.join(CLI2)
self.pipeline = Gst.parse_launch(gcmd)
self.hlssink = self.pipeline.get_by_name('sink')
self.hlssink.set_property('target-duration', 2)
self.hlssink_pad = self.hlssink.get_static_pad('sink')
probe_id = self.hlssink_pad.add_probe(Gst.PadProbeType.EVENT_UPSTREAM,
    probe_callback)
Gstreamer message to signal new frame from video source (webcam)