Streaming video from OpenCV through gstreamer to VLC via RTSP

Question

I would like to stream a video source using opencv and gstreamer on a PI 3b. From code online I got this far, and can not seem to find or debug the issue. out.IsOpened() always returns False. The video does show locally with imshow.

import cv2

cap = cv2.VideoCapture('sample-mp4-file.mp4')

# Get video dimensions
frame_width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
frame_height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
fps = int(cap.get(cv2.CAP_PROP_FPS))

pipeline = 'appsrc ! videoconvert ! videoscale ! video/x-raw,width=640,height=480 ! x264enc speed-preset=veryfast tune=zerolatency bitrate=800 ! rtspclientsink location=rtsp://localhost:8554/mystream '
out = cv2.VideoWriter(pipeline, cv2.CAP_GSTREAMER, 0, fps, (frame_width, frame_height))

print(out.isOpened())
print()

while cap.isOpened():
    ret, frame = cap.read()
    if ret:
        # Display the frame
        cv2.imshow('Video Stream', frame)
        out.write(frame)
        print(out.isOpened())

        if cv2.waitKey(int(1000/fps)) & 0xFF == ord('q'):
            break
    else:
        break

# Release everything if job is finished
cap.release()
out.release()

With out never open nothing happens on the connection side. I never see an incoming connection. From the command line, this does work

gst-launch-1.0 filesrc location=sample-mp4-file.mp4 ! decodebin ! videoconvert ! videoscale ! video/x-raw,width=640,height=480 ! x264enc speed-preset=veryfast tune=zerolatency bitrate=800 ! rtspclientsink location=rtsp://localhost:8554/mystream

I downloaded the sample mp4 from here

To serve the rtsp stream I'm using mediamtx found here. I can then view the stream from a connected PC using VLC.

EDIT:

Currently it seems like I'm missing support for gstreamer in opencv (An error would have been nice...)

import cv2
print(cv2.getBuildInformation())

output:

  Video I/O:
    DC1394:                      NO
    FFMPEG:                      YES
      avcodec:                   YES (59.37.100)
      avformat:                  YES (59.27.100)
      avutil:                    YES (57.28.100)
      swscale:                   YES (6.7.100)
      avresample:                NO
    GStreamer:                   NO
    v4l/v4l2:                    YES (linux/videodev2.h)

It takes forever to rebuild, so will repost tomorrow when it's done.

Answer 1

After quite a few attempts, I was able to compile opencv from source on the raspberry pi 3b to have gstreamer support. This solved my problem.

I used this tutorial but updated to latest version of opencv, disabled support for opencl as I could not get it to work, changed qt to version 5, and added support for GTK all done in the CMAKEFLAGS part of the script. Make sure you have a BIG swap file (mine was 5 GB). You can also increase the jobs count. I made mine 3 and it worked fine.