# VideoCapture not working with Gstreamer pipeline

**URL:** <https://forum.opencv.org/t/videocapture-not-working-with-gstreamer-pipeline/12188>\
**Category:** Python\
**Tags:** gstreamer, videoio\
**Created:** [March 1, 2023, 12:45am UTC](https://forum.opencv.org/t/videocapture-not-working-with-gstreamer-pipeline/12188 "2023-03-01T00:45:03Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![Fourier](https://avatars.discourse-cdn.com/v4/letter/f/7ea924/32.png) [@Fourier](https://forum.opencv.org/u/Fourier)\
**Post date:** [March 1, 2023, 12:45am UTC](https://forum.opencv.org/t/videocapture-not-working-with-gstreamer-pipeline/12188/1 "2023-03-01T00:45:03Z")

</div>

I have written a function to display two stereo cameras with different camera ids. I am later feeding those id’s into videocapture function. I can see that one camera is live-streaming and says both camera’s are open but rest of the program is not working. Can someone please direct me what I am missing here? Here is my program:

```
import cv2
import gi
gi.require_version("Gst", "1.0")
from gi.repository import Gst, GLib

#Initialize GStreamer
Gst.init(None)

def display_camera(camera_id):
  pipeline = Gst.Pipeline.new("video-display")

  # create element
  source = Gst.ElementFactory.make("qtiqmmfsrc", "qmmf-source")
framefilter = Gst.ElementFactory.make("capsfilter", "frame-filter")
sink = Gst.ElementFactory.make("waylandsink", "display")

if not pipeline or not source or not framefilter or not sink:
    print("Create element failed")
    return

source.set_property("camera", camera_id)

# Modify the properties for framefilter
if camera_id == 0:
    framefilter.set_property("caps",
                             Gst.caps_from_string("video/x-raw,format=NV12,framerate=30/1,width=1920,height=1080"))
else:
    framefilter.set_property("caps",
                             Gst.caps_from_string("video/x-raw,format=NV12,framerate=30/1,width=1280,height=720"))

# Modify the properties for sink
sink.set_property("x", 200)
sink.set_property("y", 200)
sink.set_property("width", 1280)
sink.set_property("height", 720)

# Build the pipeline
pipeline.add(source)
pipeline.add(framefilter)
pipeline.add(sink)

if not source.link(framefilter):
    print("ERROR: Could not link source to framefilter")
    return
if not framefilter.link(sink):
    print("ERROR: Could not link framefilter to sink")
    return

# Start playing
pipeline.set_state(Gst.State.PLAYING)
print("Started Liveview for camera %d" % camera_id)

return pipeline

# Start display pipelines for the cameras
camera_id1 = 1
pipeline_str = display_camera(camera_id1)

camera_id2 = 2
pipeline_str2 = display_camera(camera_id2)

# Open video capture for recording
cap1 = cv2.VideoCapture(display_camera(camera_id1))
cap2 = cv2.VideoCapture(display_camera(camera_id2))

#I tried this earlier but it is saying Videocapture takes only one argument so I used above command
#cap1 = cv2.VideoCapture(pipeline_str, cv2.CAP_GSTREAMER)
#cap2 = cv2.VideoCapture(pipeline_str2, cv2.CAP_GSTREAMER)

# Check if the video capture objects were successfully opened
if not cap1.isOpened() or not cap2.isOpened():
    print("Failed to open cameras for recording")
    exit()

  num = 0

while True:
    success1, img1 = cap1.read()
    success2, img2 = cap2.read()

  if not success1 or not success2:
    print("Failed to read from cameras")
    break

k = cv2.waitKey(5)

if k == 27:
    break
elif k == ord('s'): # wait for 's' key to save and exit
    cv2.imwrite('images/stereoLeft/imageL' + str(num) + '.png', img1)
    cv2.imwrite('images/stereoright/imageR' + str(num) + '.png', img2)
    print("images saved!")
    num += 1

cv2.imshow('Camera 1', img1)
cv2.imshow('Camera 2', img2)

# Check for keyboard input
if cv2.waitKey(1) == 27:
    break

# Stop and cleanup the pipelines
pipeline_str.set_state(Gst.State.NULL)
pipeline_str2.set_state(Gst.State.NULL)

 # Release and destroy all windows before termination
cap1.release()
cap2.release()
cv2.destroyAllWindows()

```

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<div class="post-metadata">

**Author:** ![berak](https://avatars.discourse-cdn.com/v4/letter/b/85f322/32.png) [@berak](https://forum.opencv.org/u/berak)\
**Post date:** [March 1, 2023, 7:32am UTC](https://forum.opencv.org/t/videocapture-not-working-with-gstreamer-pipeline/12188/2 "2023-03-01T07:32:19Z")

</div>

most likely, it’s an usb bandwidth problem,  
a single usb hub can barely handle a single hires cam.

try to use different usb _hubs_ for the 2 cams, or reduce the resolution, if that works, you’ll know …

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<div class="post-metadata">

**Author:** ![Fourier](https://avatars.discourse-cdn.com/v4/letter/f/7ea924/32.png) [@Fourier](https://forum.opencv.org/u/Fourier)\
**Post date:** [March 1, 2023, 7:48pm UTC](https://forum.opencv.org/t/videocapture-not-working-with-gstreamer-pipeline/12188/3 "2023-03-01T19:48:37Z")

</div>

I am using MIPI OV9282 camera’s on Qualcomm’s rb5 board. They both have separate access. When I am running above code, it shows this log: Here is the log and I can see one window open with live camera access.

```
gbm_create_device(156): Info: backend name is: msm_drm
Started Liveview for camera 1
gbm_create_device(156): Info: backend name is: msm_drm
Started Liveview for camera 2
gbm_create_device(156): Info: backend name is: msm_drm
Started Liveview for camera 1

```

But I think rest of the code is not running, because probably OpenCVCapture is not taking livestream? I don’t know what I can change to fix this.

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<div class="post-metadata">

**Author:** ![Fourier](https://avatars.discourse-cdn.com/v4/letter/f/7ea924/32.png) [@Fourier](https://forum.opencv.org/u/Fourier)\
**Post date:** [March 7, 2023, 7:41am UTC](https://forum.opencv.org/t/videocapture-not-working-with-gstreamer-pipeline/12188/4 "2023-03-07T07:41:29Z")

</div>

can someone help me with this please?

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<div class="post-metadata">

**Author:** ![Chris2L](https://avatars.discourse-cdn.com/v4/letter/c/45deac/32.png) [@Chris2L](https://forum.opencv.org/u/Chris2L)\
**Post date:** [August 1, 2023, 11:42am UTC](https://forum.opencv.org/t/videocapture-not-working-with-gstreamer-pipeline/12188/5 "2023-08-01T11:42:56Z")

</div>

Hi @Fourier  
I can unfortunately not comment on your question, but how do you feed a pipeline into cv2.VideoCapture? This should not be possible as the first argument should be a str and not a Pipeline. Not sure how your code sample is actually showing one stream.

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<div class="post-metadata">

**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [August 1, 2023, 5:58pm UTC](https://forum.opencv.org/t/videocapture-not-working-with-gstreamer-pipeline/12188/6 "2023-08-01T17:58:49Z")

</div>

Fourier’s code doesn’t even do that. his `display_camera()` function returns nothing.

that entire code should be questioned.

VideoCapture _can_ take a string describing a pipeline, as is shown in all the examples that demonstrate gstreamer in opencv.