How to use Gstreamer pipeline in OpenCV ?

http://answers.opencv.org/question/202017/how-to-use-gstreamer-pipeline-in-opencv/?answer=202087#post-id-202087

How to use Gstreamer pipeline in OpenCV ?

I have OpenCV installed with ffmpeg and gstreamer support.
I have a working Gstreamer pipeline from my raspberry pi 3b to Ubuntu 16.04.

This is my Gstreamer pipeline SEND script line on the Raspberry Pi 3b:
gst-launch-1.0 -v v4l2src ! video/x-raw,width=320,height=240 ! videoconvert ! jpegenc ! rtpjpegpay ! udpsink host=192.168.1.101 port=5200

This is my Gstreamer pipeline RECEIVER script line at the Ubuntu 16.04 end:
gst-launch-1.0 -v udpsrc port=5200 ! application/x-rtp, encoding-name=JPEG,payload=26 ! rtpjpegdepay ! jpegdec ! videoconvert ! autovideosink

This pipeline produces a good quality low latency video-stream.

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Test this :

import numpy as np import cv2 from multiprocessing import Process
then:

def send():
    cap_send = cv2.VideoCapture('videotestsrc ! video/x-raw,framerate=20/1 ! videoscale ! videoconvert ! appsink', cv2.CAP_GSTREAMER)
    out_send = cv2.VideoWriter('appsrc ! videoconvert ! x264enc tune=zerolatency bitrate=500 speed-preset=superfast ! rtph264pay ! udpsink host=127.0.0.1 port=5000',cv2.CAP_GSTREAMER,0, 20, (320,240), True)

    if not cap_send.isOpened() or not out_send.isOpened():
        print('VideoCapture or VideoWriter not opened')
        exit(0)

    while True:
        ret,frame = cap_send.read()

        if not ret:
            print('empty frame')
            break

        out_send.write(frame)

        cv2.imshow('send', frame)
        if cv2.waitKey(1)&0xFF == ord('q'):
            break

    cap_send.release()
    out_send.release()

def receive():
    cap_receive = cv2.VideoCapture('udpsrc port=5000 caps = "application/x-rtp, media=(string)video, clock-rate=(int)90000, encoding-name=(string)H264, payload=(int)96" ! rtph264depay ! decodebin ! videoconvert ! appsink', cv2.CAP_GSTREAMER)

    if not cap_receive.isOpened():
        print('VideoCapture not opened')
        exit(0)

    while True:
        ret,frame = cap_receive.read()

        if not ret:
            print('empty frame')
            break

        cv2.imshow('receive', frame)
        if cv2.waitKey(1)&0xFF == ord('q'):
            break

    #cap_receive.release()

if __name__ == '__main__':
    s = Process(target=send)
    r = Process(target=receive)
    s.start()
    r.start()
    s.join()
    r.join()

    cv2.destroyAllWindows()