Seeking Reference Code for MPA Integration with RTSP Video Streams for TFLite Server

Ethan Wu

@Alex-Kushleyev Originally, I was thinking of achieving simple image transmission by modifying the example code under libmodal-pipe, and then connecting it to both MPA and the tflite server. Would you advise against this approach?

Alex Kushleyev

@Ethan-Wu , publishing an image using MPA is easy. How were you planning to handle the RTSP video stream and converting the output to YUV?

An example of publishing various image types (gray, rgb) can be found in voxl-camera-server source code. The example you referenced is a generic one, there is more specific API for publishing images.

create the publisher: https://gitlab.com/voxl-public/voxl-sdk/services/voxl-camera-server/-/blob/master/src/hal3_camera_mgr.cpp?ref_type=heads#L2161 , you just need to call pipe_server_create.. in short...

pipe_info_t info;
strcpy(info.name       , "my_new_camera");
strcpy(info.type       , "camera_image_metadata_t");
strcpy(info.server_name, "my_test_app");
info.size_bytes = 64*1024*1024;  //pipe buffer size in bytes
int pipe_id     = pipe_server_get_next_available_channel(); #pipe id to use for publishing
int flags       = 0;
pipe_server_create(pipe_id, info, flags);

publish : https://gitlab.com/voxl-public/voxl-sdk/services/voxl-camera-server/-/blob/master/src/hal3_camera_mgr.cpp?ref_type=heads#L934 (please take a look at the camera_image_metadata_t in libmodal_pipe headers. there is a timestamp and other fields that are not directly filled in this example (they are filled elsewhere).

short example (assuming image is just raw8):

int publish_image(uint8_t * image_data, uint32_t width, uint32_t height)
{
  camera_image_metadata_t meta;
  meta.magic_number = CAMERA_MAGIC_NUMBER;
  meta.frame_id = 0; //TODO fill in the frame id / counter
  meta.width  = width;
  meta.stride = width;
  meta.height = height;
  meta.size_bytes = meta.width * meta.height;
  meta.format = IMAGE_FORMAT_RAW8;
  meta.timestamp_ns = 0; //TODO: fill in correct timestamp
  meta.exposure_ns = 0; //TODO: fill in exposure info if available
  meta.gain = 0; //TODO: fill in gain info if available

  return pipe_server_write_camera_frame(pipe_id, meta, image_data);
}

The full definition of camera_image_metadata_t can be found here : https://gitlab.com/voxl-public/voxl-sdk/core-libs/libmodal-pipe/-/blob/master/library/include/modal_pipe_interfaces.h#L190

Ethan Wu

@Alex-Kushleyev
Hi, thanks for replying, that really helps. I was intended to use opencv C++ to read rtsp stream, at least to read a local video for testing. I looked into voxl-mpa-tools which makes use of voxl-opencv as one of its dependency, and wrote a simple program to read video source like below :

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main() {
    string filename;
    cout << "Enter the file name of the video: ";
    cin >> filename;

    VideoCapture cap(filename);

    if (!cap.isOpened()) {
        cerr << "Error: Unable to open video file." << endl;
        return -1;
    }
    // play video on local host
}

While it can played both mp4 and RTSP source on my PC, isOpened always returns False on voxl.

I also install python3 and opencv-python on voxl and test it out, but it's able to open mp4 but failed to read RTSP. That goes same on my PC, so I might get something wrong.

I have used ffmpeg to confirm that the RTSP URL is correct, so I don't think it's a problem with the URL being incorrect.

Ethan Wu

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

Alex Kushleyev

@Ethan-Wu ,

I have not tested using opecv in c++ to receive the RTSP streams, but i have tested the same thing in python3 with opencv on VOXL2. I also found that video capture did not work if i just provided the rtsp stream location as the "filename". It turns out that on VOXL2, the opencv video capture uses gstreamer (not sure about PC), so i had to tell opencv what gstreamer pipeline to use. Specifically, here is the the snippet of the python code that i tested to receive h264 stream that was actually generated by voxl-camera-server on VOXL2 (i have not tested h265 this way). You can test out a similar approach in C++

import cv2
stream_url = 'rtsp://127.0.0.1:8900/live'

#using software decoder (i think)
stream = 'gst-launch-1.0 rtspsrc location=' + stream_url + ' latency=0 ! queue ! rtph264depay ! h264parse ! avdec_h264 ! autovideoconvert ! appsink'

#using hardware decoder
#stream = 'gst-launch-1.0 rtspsrc location=' + stream_url + ' latency=0  ! queue ! rtph264depay ! h264parse ! qtivdec turbo=true ! autovideoconvert ! appsink'

vcap = cv2.VideoCapture(stream,cv2.CAP_GSTREAMER)

while(1):
    ret, frame = vcap.read()
    #check ret and process image...

Please note that the current version of opencv installed on voxl2 does not have python3 bindings, but i enabled that in order to use opencv in Python3. We will probably update the opencv voxl2 deb package soon to include the python3 bindings.

Ethan Wu

@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?

Ethan Wu

@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

@Ethan-Wu,

Gstreamer on voxl2 has customizations to make use of voxl2 hardware (video encoder, decoder), so i am not sure if standard gstreamer installation would work. Perhaps that is why you are seeing issues with the standard installation of gstreamer.

Alex Kushleyev

I wrote some examples how to use use python3 to get external rtsp stream into python using opencv (which uses gstreamer) and then publish RGB image via MPA.

This requires updated version of the opencv package for VOXL2 with python3 bindings (i have not published that yet). there is also an experimental interface to get and send images via MPA (using pympa python bindings).

If you are interested trying out this option, we can explore it

Ethan Wu

@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.

Alex Kushleyev

@Ethan-Wu , can you clarify the gstreamer freezing issue? Are you saying that the client side freezes? what source are you using as the rtsp server?

In my testing the above python scripts, i found that if the rtsp stream is generated using a combination of voxl-camera-server and voxl-streamer then the gstreamer client does freeze occasionally. I will investigate this at some point soon.

However, there is a 3rd party app that allows you to use gstreamer on the server side and i did not experience client freezing with that option. In this case, gstreamer server side is also on voxl2 and it is using a qtiqmmfsrc plugin to get video from the camera pipeline.

#start rtsp server using gst-rtsp-launch ( https://github.com/sfalexrog/gst-rtsp-launch )
gst-rtsp-launch -p 8900 -e live "( qtiqmmfsrc camera=0 name=hires ! video/x-h264,format=NV12,width=1920,height=1080,framerate=30/1 ! queue ! h264parse ! rtph264pay name=pay0 pt=96 )"

Ethan Wu

@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.

Ethan Wu

@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

@Ethan-Wu ,

Hmm. When i tested with a local rtsp stream generated on the same voxl2, the video capture started immediately. The freezing would occur in the python client side sometime after i got a bunch of frames (when using voxl-streamer to produce the rtsp stream). When the freezing happened, it looked like voxl-streamer dropped the client connection for some reason. I will test with a local ip cam that is producing rtsp today.

It seems gstreamer rtsp receiving end may not be running correctly on your end. How about i share with you updated native opencv package with python bindings and you could try running this natively on voxl2 without your environment? This whay you can test what I am testing.

Alex Kushleyev

I just tried playing a local rtsp stream from an ip cam (using rtsp_rx_mpa_pub.py) and it initially starts playing but gets stuck after a few seconds. However, changing the pipeline to use the following (using avdec_h264 instead of qtivdec:

 .... rtph264depay ! h264parse config-interval=-1 ! avdec_h264 ! autovideoconvert ! appsink

Does not get stuck.

So there must be something about the hw decoder that causes it to get stuck, I will investigate further..

Ethan Wu

@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.

Alex Kushleyev

@Ethan-Wu , I uploaded the opencv deb here : https://storage.googleapis.com/modalai_public/temp/voxl2-misc-packages/voxl-opencv_4.5.5-3_arm64.deb

it was built using this branch of voxl-opencv project : https://gitlab.com/voxl-public/voxl-sdk/third-party/voxl-opencv/-/tree/add-python3-bindings/

You can just install that deb to overwrite your existing opencv installation and try the python scripts for rtsp natively on voxl2

By the way, how do you get gstreamer to output that debug info? does it automatically print it if there is an issue?

Ethan Wu

@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

Ethan Wu

@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:

Screenshot from 2024-03-22 17-55-03.png

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

Alex Kushleyev

@Ethan-Wu , yes the installation of opencv .deb should be done use dpkg -i <package.deb>.

When you installed the newer version of Gstreamer, did you overwrite the existing one or did the new version go into another location?

it seems the new version of Gstreamer is not functioning correctly.

You should be able to test the gstreamer using command line pipeline like this (without python) and just dump the frames to stdout:

gst-launch-1.0 rtspsrc location=rtsp://127.0.0.1:8900/live latency=0 ! queue ! rtph264depay ! h264parse ! avdec_h264 ! videoconvert ! filesink location=/dev/stdout

If that is not working, then you may want to reflash VOXL2 back to original state, i am not sure how to recover the original gstreamer.