Image Serving Event

[Dende]

Hi,

I'm pretty new to Gstreamer development.  I am working on an image
processing tester.  The gstreamer app posts jpeg's in an h264 stream to the
unit being tested via rtp (see how the unit being tested processes a
standardized set of jpeg images coming in a h264 stream).  In order for this
to work I need to know when the images are first being served to the unit. 
I have all the jpeg streaming protocol working and I can push new images, I
can't figure out how to trigger an event to tell me when the image is going
through the sink for the first time.

Code is in Python.  I will include some relevant snippets.

Thanks!

class SenderImages:
    def __init__(self):
        # Control if it is allowed push buffer in queue using "need-data"
and "enough-data" signals
        self.is_push_buffer_allowed = None
        self._mainloop = GObject.MainLoop()
        auto_video_sink_pipeline = "appsrc name=source !
image/jpeg,framerate=(fraction)" + str(framerate) + "/1  ! jpegdec !
videoconvert ! videoscale ! capsfilter caps=video/x-raw,width=" + image_w +
",height=" + image_h + " ! x264enc ! rtph264pay ! multiudpsink clients=" + 
Image_Stream_URIs 
        self._pipeline = Gst.parse_launch(auto_video_sink_pipeline)
        self._src = self._pipeline.get_by_name('source')
        self._src.connect('need-data', self.start_feed)
        self._src.connect('enough-data', self.stop_feed)
        self._src.set_property('format', 'time')
        self._src.set_property('do-timestamp', True)

    def start_feed(self, src, length):
        # print('======================> need data length: %s' % length)
        self.is_push_buffer_allowed = True

    def stop_feed(self, src):
        # print('======================> enough_data')
        self.is_push_buffer_allowed = False

    def play(self):
        self._pipeline.set_state(Gst.State.PLAYING)

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

    def run(self):
        """ Run - blocking. """
        self._mainloop.run()

    # def push(self):
    def push(self, filename):
        """ Push a buffer into the source. """
        import os
        if self.is_push_buffer_allowed:

            handle = open(filename, "rb");
            data = handle.read()
            handle.close()
            # Allocate GstBuffer
            buf = Gst.Buffer.new_allocate(None, len(data), None)
            buf.fill(0, data)
            # Add buffer metadata
            write_meta(buf, filename)
            # Create GstSample
            sample = Gst.Sample.new(buf,
Gst.caps_from_string("image/jpeg,framerate=(fraction)" + str(framerate) +
"/1"),
                                    None, None)
            # Push Sample on appsrc
            gst_flow_return = self._src.emit('push-sample', sample)

            if gst_flow_return != Gst.FlowReturn.OK:
                print('We got some error, stop sending data')

        else:
            print('It is enough data for buffer....')




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