OpenCV Video Capture with GStreamer doesn’t work but work on terminal

Autonomous Machines Jetson & Embedded Systems Jetson Nano
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For better advice, you may post the exact command or code that that you’re trying and error messages that you’re facing, so that your case can be easily reproduced.

First be sure that your python env has an opencv version supporting GStreamer:

import cv2
print(cv2.getBuildInformation())

If it shows Gstreamer SUPPORT YES, then you can get further.

Try:

import cv2

# Reading BGRx frames into opencv:
cap = cv2.VideoCapture("nvarguscamerasrc ! video/x-raw(memory:NVMM),width=3264, height=2464, framerate=21/1, format=NV12 ! nvvidconv ! video/x-raw,format=BGRx ! appsink drop=1", cv2.CAP_GSTREAMER)

# Or reading BGR frames as expected by most opencv algorithms:
# cap = cv2.VideoCapture("nvarguscamerasrc ! video/x-raw(memory:NVMM),width=3264, height=2464, framerate=21/1, format=NV12 ! nvvidconv ! video/x-raw,format=BGRx ! videoconvert ! video/x-raw,format=BGR ! appsink drop=1", cv2.CAP_GSTREAMER)

if not cap.isOpened():
    print("failed to open video capture")
    exit(-1)

cv2.namedWindow("CamPreview", cv2.WINDOW_AUTOSIZE)

frames=0
# Run for 10s @21fps
while frames < 210:
   ret_val, img = cap.read();
   if not ret_val:
       print("failed to read from video capture")
       break
   frames = frames + 1

   cv2.imshow('CamPreview',img)

   if cv2.waitKey(1) == ord('q'):
       break
 
cv2.destroyAllWindows()
cap.release()

If this works, you may try resizing into lower resolution.
Note that nvvidconv may not be able to scale into huge factors (but multiple nvviconv rescaling stages may work).
I notice that your gst-launch command uses 320x240 while your opencv example uses 224x224.

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