it takes longer time to generate thumbnail by gstreamer enginee than before

attach root cause,

At line 118 in function __seek_for_frame, should follow a "break", one frame is enough for thumbnail creating. Otherwise repeat 5 times.
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        for location in frame_locations:
            abs_location = int(location * duration)
            event = self._pipeline.seek(1.0, gst.FORMAT_TIME,
                                        gst.SEEK_FLAG_FLUSH | gst.SEEK_FLAG_KEY_UNIT,
                                        gst.SEEK_TYPE_SET, abs_location,
                                        gst.SEEK_TYPE_NONE, 0)
            if not event:
              raise VideoFrameError("Not Seekable")

            if not self.set_state_blocking(self._pipeline, gst.STATE_PAUSED):
                raise VideoFrameError("Not Pausable")
            frame = self._sink.get_current_frame()
            img = Image.frombuffer("RGB", sink_size, frame, "raw", "RGB", 0, 1)
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