Can not trigger "on-receiving-rtcp" event to get RTCP packet

[Mathieu Duponchelle]

Why are you requesting the pad in the first place?

On Sun, 2023-05-21 at 15:27 +0800, Max Weng via gstreamer-devel wrote:
> Hi, 
> 
>     I am currently exploring the possibilities of using GStreamer for
> a project, a territory that is relatively new to me. I am convinced,
> however, that GStreamer is an ideal fit for my objectives.
> 
> The task at hand is to extract server timestamps from RTCP packets.
> For this, I referred to the article, Absolute Timestamp of Arbitrary
> Frame in RTSP Stream with GStreamer
> 
>   I have been running into some difficulties during the
> implementation phase.
> 
> I am experiencing an inconsistent triggering of the "on-receiving-
> rtcp" event. It appears to get activated only sporadically,
> approximately once in every 20 attempts. This inconsistency makes it
> challenging for me to proceed effectively with the project.
> 
> In addition, an error message always presents itself: "Element
> manager already has a pad named recv_rtcp_sink_0, the behaviour of
> gst_element_get_request_pad() for existing pads is undefined!". This
> error is making the situation even more complex to understand and
> resolve.
> 
> I would truly appreciate it if you could provide some insights or
> suggestions regarding these issues. I am eager to understand what
> might be causing these problems, and how best to address them.
> 
>   here is my code test_gstreamer.py:
> 
> import datetime
> import pickle
> from multiprocessing.connection import Connection
> import threading
> 
> from time import sleep
> import gi
> from log import setup_custom_logger
> 
> gi.require_version("Gst", "1.0")
> gi.require_version("GstRtp", "1.0")
> gi.require_version("GstVideo", "1.0")
> 
> from gi.repository import GLib, GObject, Gst, GstRtp, GstVideo #
> noqa:F401,E402
> 
> logger = setup_custom_logger(__name__)
> 
> GObject.threads_init()
> Gst.init()
> 
> url = 'rtsp://localhost:8554/mystream'
> pipeline = ''
> 
> 
> def fly():
>  main_loop = GLib.MainLoop()
>  main_loop_thread = threading.Thread(target=main_loop.run)
>  main_loop_thread.start()
>  command = f"rtspsrc name=rtspsrc location={url} protocols=tcp
> latency=10 max-rtcp-rtp-time-diff=10 ! errorignore ! rtph265depay
> name=depay ! appsink name=sink"
>  pipeline = Gst.parse_launch(command)
>  bus = pipeline.get_bus()
>  bus.add_signal_watch()
>  bus.connect("message", on_message)
>  bus.enable_sync_message_emission()
> 
>  rtspsrc = pipeline.get_by_name("rtspsrc")
>  rtspsrc.connect("new-manager", on_new_manager)
>  depay = pipeline.get_by_name("depay")
>  sinkpad = depay.get_static_pad("sink")
>  probeID = sinkpad.add_probe(
>  Gst.PadProbeType.BUFFER, calculate_timestamp)
> 
>  pipeline.set_state(Gst.State.PLAYING)
> 
>  try:
>  while True:
>  sleep(0.1)
>  except KeyboardInterrupt:
>  pass
> 
>  pipeline.set_state(Gst.State.NULL)
>  main_loop.quit()
>  main_loop_thread.join()
> 
> 
> def calculate_timestamp(pad, info):
>  return Gst.PadProbeReturn.OK
> 
> 
> def on_new_manager(rtspsrc, manager):
>  logger.info(f"on_new_manager")
>  sinkpad = manager.get_request_pad("recv_rtcp_sink_0")
>  session = manager.emit("get-internal-session", 0)
>  session.connect("on-receiving-rtcp", on_receive_rtcp)
> 
> 
> def on_receive_rtcp(session, buffer: Gst.Buffer):
>  logger.info("on_receive_rtcp")
>  logger.info(buffer)
>  rtcp_buffer = GstRtp.RTCPBuffer()
>  res = GstRtp.RTCPBuffer.map(buffer, Gst.MapFlags.READ, rtcp_buffer)
>  rtcp_packet = GstRtp.RTCPPacket()
>  rtcp_buffer.get_first_packet(rtcp_packet)
> 
>  while True:
>  if rtcp_packet.get_type() == GstRtp.RTCPType.SR:
>  logger.info(rtcp_packet)
>  si = rtcp_packet.sr_get_sender_info()
>  ntp_time = si[1]
>  rtp_time = si[2]
>  logger.info("ntp_time: %d, rtp_time: %d", ntp_time, rtp_time)
>  if rtcp_packet.move_to_next() == False:
>  break
> 
> 
> def on_message(bus: Gst.Bus, message: Gst.Message):
>  mtype = message.type
>  # TODO handle message
> 
> 
> if __name__ == "__main__":
>  fly()
> 
> 
> here is how I run a local RSTP server:
> $ docker run --rm -it --network=host aler9/rtsp-simple-server
> $ while true; do gst-launch-1.0 rtspclientsink name=s
> location=rtsp://localhost:8554/mystream
>  filesrc location=//path/to/video.mp4
>  ! qtdemux name=d d.video_0 ! queue ! s.sink_0 d.audio_0 ! queue ! 
> s.sink_1 ; done
> 
> here is the output from my code, no "on-receiving-rtcp" triggered:
> $ python test_gstreamer.py 
> test_gstreamer.py:19: PyGIDeprecationWarning: Since version 3.11,
> calling threads_init is no longer needed. See:
> https://wiki.gnome.org/PyGObject/Threading
>   GObject.threads_init()
> 2023-05-21 15:05:06,467 - __main__ - INFO - on_new_manager
> 
> (python:96503): GStreamer-CRITICAL **: 15:05:06.469: Element manager
> already has a pad named recv_rtcp_sink_0, the behaviour of
>  gst_element_get_request_pad() for existing pads is undefined!
> 
> here is output with "on-receiving-rtcp" triggered:
> $ python test_gstreamer.py 
> test_gstreamer.py:19: PyGIDeprecationWarning: Since version 3.11,
> calling threads_init is no longer needed. See:
> https://wiki.gnome.org/PyGObject/Threading
>   GObject.threads_init()
> 2023-05-21 15:05:10,382 - __main__ - INFO - on_new_manager
> 
> (python:96548): GStreamer-CRITICAL **: 15:05:10.384: Element manager
> already has a pad named recv_rtcp_sink_0, the behaviour of 
> gst_element_get_request_pad() for existing pads is undefined!
> 2023-05-21 15:05:11,730 - __main__ - INFO - on_receive_rtcp
> 2023-05-21 15:05:11,730 - __main__ - INFO - <Gst.Buffer object at
> 0x7fbf3a6918e0 (GstBuffer at 0x166cc60)>
> 2023-05-21 15:05:11,732 - __main__ - INFO - <GstRtp.RTCPPacket object
> at 0x7fbf39c49860 (void at 0x7fbf2c08b390)>
> 2023-05-21 15:05:11,732 - __main__ - INFO - ntp_time:
> 16723062952823484284, rtp_time: 4125066893
>