Write in Gstreamer pipeline from opencv in python

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Write in Gstreamer pipeline from opencv in python

I'm trying to stream some images form opencv using gstreamer and I got ome issues with the pipeline. I'm new to gstreamer and opencv in general. I compiled opencv 3.2 with gstreamer for python3 on a raspberry pi 3. I have a little bash script that I use with raspivid
    raspivid -fps 25 -h 720 -w 1080 -vf -n -t 0 -b 2000000 -o - | gst-launch-1.0 -v fdsrc ! h264parse ! rtph264pay config-interval=1 pt=96 ! gdppay ! tcpserversink host= port=5000

I wanted to translate this pipeline in order to use it from opencv and feed into it images that my algorithm manipulates. I did some research and figured that I can use videoWriter with appsrc instead of fdsrc but I get the following error
    GStreamer Plugin: Embedded video playback halted; module appsrc0 reported: Internal data flow error.

The python script that I came up with is the following by the way
    import cv2
    cap = cv2.VideoCapture(0)
    # Define the codec and create VideoWriter object
    fourcc = cv2.VideoWriter_fourcc(*'MJPG')
    out = cv2.VideoWriter('appsrc  ! h264parse ! '
                          'rtph264pay config-interval=1 pt=96 ! '
                          'gdppay ! tcpserversink host= port=5000 ',
                          fourcc, 20.0, (640, 480))
    while cap.isOpened():
        ret, frame = cap.read()
        if ret:
            frame = cv2.flip(frame, 0)
            # write the flipped frame
            if cv2.waitKey(1) & 0xFF == ord('q'):
    # Release everything if job is finished

Is there any error in the pipeline? I don't understand the error. I already have a Python client that can read from the bash pipeline and the result are pretty good from the latency perspective and consumed resources .