@Alex-Kushleyev
Hi, thank you for your assistance over the past few days. I am now able to successfully stream videos from Trip to Voxl and QGC using the code I provided earlier, combined with pympa. The decoding issue I mentioned occurred because the video streamed from Trip2 was in YUV420 format, but I reshaped the data in RGB format.

As for the original method using OpenCV + GStreamer, I am still unsure where the problem lies. It could be a decoding issue or an installation problem with OpenCV and GStreamer. Additionally, there were many unexpected situations related to GStreamer during the research process that have not yet been resolved. If I manage to identify the source of the problem, I will provide further information.

@Alex-Kushleyev
Hi,
Do I just need to upload it to voxl and dpkg -i opencv.deb so that it will overwrite my opencv-python? I did so and failed to start the steam as expected.

Also, I searched for some other replacement for opencv and got the code below :

import gi
gi.require_version('Gst', '1.0')
from gi.repository import Gst, GObject, GLib
import numpy as np
import time
import cv2
import sys

# Initialize GStreamer
Gst.init(None)

# Define the RTSP stream URL
stream_url = 'rtsp://192.168.0.201:554/live0'

# Create a GStreamer pipeline
pipeline = Gst.parse_launch(f"rtspsrc location={stream_url} latency=0 ! rtph264depay ! h264parse ! avdec_h264 ! videoconvert ! appsink")

# Start the pipeline
pipeline.set_state(Gst.State.PLAYING)

# Main loop to read frames from pipeline and publish them to MPA
frame_cntr = 0
while True:
    # Retrieve a frame from the pipeline
    sample = pipeline.get_by_name('appsink0').emit('pull-sample')
    buffer = sample.get_buffer()
    result, info = buffer.map(Gst.MapFlags.READ)
    if result:
        # Convert the frame to numpy array
        data = np.ndarray((info.size,), dtype=np.uint8, buffer=info.data)
        frame = np.reshape(data, (640, 720, 3))
        # Increment frame counter
        frame_cntr += 1
        sys.stdout.write("\r")
        sys.stdout.write(f'got frame {frame_cntr} with dims {frame.shape}')
        sys.stdout.flush()
        # Publish the frame to MPA
        cv2.imshow("frame", frame)
    else:
        print("Error mapping buffer")
    # Delay for a short period to control frame rate
    if cv2.waitKey(30) == ord('q'):
        break


cv2.destroyAllWindows()
# Stop the pipeline
pipeline.set_state(Gst.State.NULL)

And I saw image like this:

Which looks like a decode error, and I will look into it next week.

@Alex-Kushleyev You can set the environment variable GST_DEBUG to the number that fits the debug level you prefer. I made it 2 so that I can see warning and error output from gst-launch-1.0, here's the reference documentation : https://gstreamer.freedesktop.org/documentation/tutorials/basic/debugging-tools.html?gi-language=c

@Alex-Kushleyev
Sharing opencv package would be great, and I also want to share how I built opencv that supports gstreamer. I looked into this issue and followed instructions here, and made sure I saw the followings information to get gstreamer working with opencv by calling cv2.getBuildInformation() :

  Video I/O:
    DC1394:                      NO
    FFMPEG:                      YES
      avcodec:                   YES (57.107.100)
      avformat:                  YES (57.83.100)
      avutil:                    YES (55.78.100)
      swscale:                   YES (4.8.100)
      avresample:                NO
    GStreamer:                   YES (1.14.5)
    v4l/v4l2:                    YES (linux/videodev2.h)

I was using conda for virtual environment and run opencv with python 3.10 (3.9 and 3.8 are also tested), and my opencv version is 4.9.0.80.

@Ethan-Wu

About the error 'unexpected reference "gst-launch-1" ', I do get the same error when I replace the gstreamer command with gst-launch-1.0 videotestsrc ! videoconvert ! autovideosink, so I think that's not a problem.

@Alex-Kushleyev
I think the client side is freezing, and I noticed that VideoCapture takes some time to complete, but ultimately hangs on cap.read(). Below is the relevant debug information:

created output pipe rtsp-debug, channel 0, flags 0
gst-launch-1.0 rtspsrc location=rtsp://169.254.4.201:554/live0 latency=0  ! queue !  rtph264depay ! h264parse config-interval=-1 ! qtivdec ! qtivtransform !  video/x-raw,format=BGR,width=1280,height=720 !  autovideoconvert ! appsink
0:00:00.000749593 14685   0x55c069b780 WARN            GST_REGISTRY gstregistrybinary.c:489:gst_registry_binary_check_magic: Binary registry magic version is different : 1.3.0 != 1.12.0
0:00:00.057125316 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:876:priv_gst_parse_yyparse: unexpected reference "gst-launch-1" - ignoring
0:00:00.057160626 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:882:priv_gst_parse_yyparse: unexpected pad-reference "0" - ignoring
0:00:00.057168959 14685   0x55c069b780 WARN     GST_ELEMENT_FACTORY gstelementfactory.c:456:gst_element_factory_make: no such element factory "rtspsrc"!
0:00:00.057173647 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:816:priv_gst_parse_yyparse: no element "rtspsrc"
0:00:00.057890325 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:901:priv_gst_parse_yyparse: link has no source [sink=@0x55c070f730]
0:00:00.057908970 14685   0x55c069b780 WARN     GST_ELEMENT_FACTORY gstelementfactory.c:456:gst_element_factory_make: no such element factory "rtph264depay"!
0:00:00.057914021 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:816:priv_gst_parse_yyparse: no element "rtph264depay"
0:00:00.057918969 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:901:priv_gst_parse_yyparse: link has no sink [source=@0x55c070f730]
0:00:00.057923292 14685   0x55c069b780 WARN     GST_ELEMENT_FACTORY gstelementfactory.c:456:gst_element_factory_make: no such element factory "h264parse"!
0:00:00.057927354 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:816:priv_gst_parse_yyparse: no element "h264parse"
0:00:00.057932250 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:901:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.057936260 14685   0x55c069b780 WARN     GST_ELEMENT_FACTORY gstelementfactory.c:456:gst_element_factory_make: no such element factory "qtivdec"!
0:00:00.057939437 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:816:priv_gst_parse_yyparse: no element "qtivdec"
0:00:00.057944072 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:901:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.057947874 14685   0x55c069b780 WARN     GST_ELEMENT_FACTORY gstelementfactory.c:456:gst_element_factory_make: no such element factory "qtivtransform"!
0:00:00.057951467 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:816:priv_gst_parse_yyparse: no element "qtivtransform"
0:00:00.057956884 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:901:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.057971726 14685   0x55c069b780 WARN     GST_ELEMENT_FACTORY gstelementfactory.c:456:gst_element_factory_make: no such element factory "autovideoconvert"!
0:00:00.057979851 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:816:priv_gst_parse_yyparse: no element "autovideoconvert"
0:00:00.057985215 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:901:priv_gst_parse_yyparse: link has no source [sink=@(nil)]
0:00:00.058182496 14685   0x55c069b780 ERROR           GST_PIPELINE grammar.y:901:priv_gst_parse_yyparse: link has no source [sink=@0x55c06f51b0]

(python:14685): GStreamer-CRITICAL **: 08:49:15.037: gst_caps_get_structure: assertion 'GST_IS_CAPS (caps)' failed

(python:14685): GStreamer-CRITICAL **: 08:49:15.038: gst_structure_get_int: assertion 'structure != NULL' failed
[ WARN:0@30.090] global cap_gstreamer.cpp:1714 open OpenCV | GStreamer warning: cannot query video width/height

(python:14685): GStreamer-CRITICAL **: 08:49:15.038: gst_structure_get_fraction: assertion 'structure != NULL' failed
[ WARN:0@30.090] global cap_gstreamer.cpp:1722 open OpenCV | GStreamer warning: cannot query video fps
[ WARN:0@30.090] global cap_gstreamer.cpp:1777 open OpenCV | GStreamer warning: Cannot query video position: status=0, value=-1, duration=-1

(python:14685): GStreamer-CRITICAL **: 08:50:20.041: gst_sample_get_caps: assertion 'GST_IS_SAMPLE (sample)' failed
[ERROR:0@95.092] global cap_gstreamer.cpp:934 retrieveVideoFrame GStreamer: gst_sample_get_caps() returns NULL

(python:14685): GStreamer-CRITICAL **: 08:51:25.042: gst_sample_get_caps: assertion 'GST_IS_SAMPLE (sample)' failed
[ERROR:0@160.094] global cap_gstreamer.cpp:934 retrieveVideoFrame GStreamer: gst_sample_get_caps() returns NULL
^C
(python:14685): GStreamer-CRITICAL **: 08:52:30.044: gst_sample_get_caps: assertion 'GST_IS_SAMPLE (sample)' failed
[ERROR:0@225.096] global cap_gstreamer.cpp:934 retrieveVideoFrame GStreamer: gst_sample_get_caps() returns NULL
Traceback (most recent call last):
  File "/voxl-mpa-tools/tools/python/rtsp_rx_mpa_pub.py", line 62, in <module>
    ret, frame = vcap.read()
KeyboardInterrupt

Today, I referenced the official website and tested the situation of OpenCV, gstreamer, and MPA with other example commands. The result is that the image produced by gst-launch-1.0 videotestsrc ! videoconvert ! autovideosink can ultimately be seen on the portal. So, I don't think it's an issue with gstreamer installation?

My RTSP source is from an external camera (edge computing device) acting as a server, connected to VOXL via Ethernet for transmission. Currently, I am not using VOXL's built-in camera or UVC camera, and I am not generating an RTSP stream through VOXL's services.

@Alex-Kushleyev

Thank you very much, that really works! And it's REALLY COOL!

Now, the remaining issue is with GStreamer support. When streaming RTSP, GStreamer often freezes without any indication or error messages, making it difficult to identify the problem. Although this may not be the most suitable question to ask here, I still want to seek advice and see if there are other ways besides blindly testing different combinations.

Thank you for your assistance.

@Ethan-Wu Or perhaps my gstreamer installation is not completely right? Here's the document I read for installation : https://gstreamer.freedesktop.org/documentation/installing/on-linux.html?gi-language=c

@Alex-Kushleyev
Hi,
I'm now able to stream rtsp with opencv-python on my PC, but fail on voxl, and I think that might be some environmental issue. I'm using conda and following this script to install gstreamer support opencv, and the program just stuck at VideoCapture() whenever start running. Here are some information after I hit ctrl+C to stop it :

^C
(python:21276): GStreamer-CRITICAL **: 07:27:40.646: 
Trying to dispose element queue0, but it is in PAUSED instead of the NULL state.
You need to explicitly set elements to the NULL state before
dropping the final reference, to allow them to clean up.
This problem may also be caused by a refcounting bug in the
application or some element.


(python:21276): GStreamer-CRITICAL **: 07:27:40.646: 
Trying to dispose element pipeline0, but it is in READY instead of the NULL state.
You need to explicitly set elements to the NULL state before
dropping the final reference, to allow them to clean up.
This problem may also be caused by a refcounting bug in the
application or some element.

[ WARN:0@1.170] global /tmp/tmp.zudKvFNc4N/opencv-python-master/opencv/modules/videoio/src/cap_gstreamer.cpp (1356) open OpenCV | GStreamer warning: unable to start pipeline
[ WARN:0@1.170] global /tmp/tmp.zudKvFNc4N/opencv-python-master/opencv/modules/videoio/src/cap_gstreamer.cpp (862) isPipelinePlaying OpenCV | GStreamer warning: GStreamer: pipeline have not been created

(python:21276): GStreamer-CRITICAL **: 07:27:40.646: 
Trying to dispose element appsink0, but it is in READY instead of the NULL state.
You need to explicitly set elements to the NULL state before
dropping the final reference, to allow them to clean up.
This problem may also be caused by a refcounting bug in the
application or some element.

Traceback (most recent call last):
  File "/playground/play.py", line 17, in <module>
    vcap = cv2.VideoCapture(stream,cv2.CAP_GSTREAMER)
KeyboardInterrupt

I'm currently dealing with it and not sure whether it's a problem from voxl or not.

Also, since MPA API is written in C++, I'm curious that even if I success to stream RTSP in python, how should I connect them?

@Alex-Kushleyev
As for converting video to YUV, I haven't reach that part, but I think opencv might be used for that conversion.