How to check if a port is opening?

$ nc -zv 192.168.1.123 4440

Connection to 192.168.1.123 4440 port [tcp/*] succeeded!

$ nc -zv 192.168.1.123 1234

^C

How to write a video using gstreamer with opencv

import numpy as np
import cv2, os

gstcmd = "https://test-videos.co.uk/vids/bigbuckbunny/mp4/h264/1080/Big_Buck_Bunny_1080_10s_1MB.mp4"

#cap = cv2.VideoCapture(gstcmd, cv2.CAP_GSTREAMER)
cap = cv2.VideoCapture(gstcmd)
count = 0
h = 1080
w = 1920

gst_out = "appsrc ! video/x-raw, format=BGR ! queue ! nvvideoconvert ! nvv4l2h264enc ! h264parse ! qtmux ! filesink location=/data/test.mp4"
out= cv2.VideoWriter(gst_out, cv2.CAP_GSTREAMER, 0, float(60), (int(1920), int(1080)))

while(True):
    try:
        count += 1
        # Capture frame-by-frame
        ret, frame = cap.read()
        if ret == False:
            break
        #frame = np.fromstring(frame, dtype=np.uint8).reshape((int(h*3/2),w,1))
        #frame = cv2.cvtColor(frame, cv2.COLOR_YUV2BGR_NV12)
        print(frame.shape)
        out.write(frame)
        # Display the resulting frame
        #cv2.imshow('frame',frame)
        #if cv2.waitKey(1) & 0xFF == ord('q'):
        #    break
    except:
        try:
            cap = cv2.VideoCapture(gstcmd, cv2.CAP_GSTREAMER)
        except:
            print("rtsp connection is down %d..." % (count))

# When everything done, release the capture

cap.release()
cv2.destroyAllWindows()