Unable to stream camera feed with OpenCV

[avdalvi2]

Hi, I am trying to stream webcam camera feed to opencv VideoCapture.

I ran the following:
sudo v4l2-ctl -d /dev/video9 --list-formats

and the output is this

ioctl: VIDIOC_ENUM_FMT
Index : 0
Type : Video Capture
Pixel Format: ‘YU12’
Name : Planar YUV 4:2:0

I had followed the commands from this:

VideoWriter with gstreamer

Hi, Please try the gst-launch-1.0 command and check if you can see video preview: $ export DISPLAY=:0 $ gst-launch-1.0 v4l2src device=/dev/video0 ! video/x-raw,format=NV12,width=640,height=512,framerate=30/1 ! videoconvert ! xvimagesink sync=0 If above command works, please apply it to cv2.VideoCapture(): cap = cv2.VideoCapture("v4l2src device=/dev/video0 ! video/x-raw,format=NV12,width=640,height=512,framerate=30/1 ! videoconvert ! video/x-raw,format=BGR ! appsink")

but I am getting the following error while starting the gstreamer:

ERROR: Pipeline doesn’t want to pause.
ERROR: from element /GstPipeline:pipeline0/GstXvImageSink:xvimagesink0: Could not initialise Xv output
Additional debug info:
xvimagesink.c(1773): gst_xv_image_sink_open (): /GstPipeline:pipeline0/GstXvImageSink:xvimagesink0:

using this command:
gst-launch-1.0 v4l2src device=/dev/video9 ! video/x-raw,format=NV12,width=640,height=512,framerate=30/1 ! videoconvert ! xvimagesink sync=0

[Honey_Patouceul]

@avdalvi2

ERROR: from element /GstPipeline:pipeline0/GstXvImageSink:xvimagesink0: Could not initialise Xv output

Seems that it failed to create X window. Are you locally logged in, with GUI and X server running ?
What gives:

echo $DISPLAY

v4l2-ctl -d /dev/video9 --list-formats-ext

Also note that NV12 format may not be correct, I’d suggest to try I420 instead for YU12.
Also note that the framerate property is not correct in the pipeline, if not just a typo when posting here you would correct it.

[avdalvi2]

I am running the Jetson in headless mode, so there is no display. So, the output of the command:

echo $DISPLAY is

and Output of v4l2-ctl -d /dev/video9 --list-formats-ext is

ioctl: VIDIOC_ENUM_FMT
Index : 0
Type : Video Capture
Pixel Format: ‘YU12’
Name : Planar YUV 4:2:0
Size: Discrete 1152x720
Interval: Discrete 0.033s (30.000 fps)

@Honey_Patouceul

I’d suggest to try I420 instead for YU12

I changed the format to I420 and now its working. More specifically I changed argument in VideoCapture function to the following:

cap = cv2.VideoCapture("v4l2src device=/dev/video9 ! video/x-raw,format=I420 ! videoconvert ! appsink")

In above line of code, 9 represents index of camera in /dev/video.
Later I encountered the following:

Gtk-WARNING **: cannot open display:

which I fixed it by running the following command in terminal

export DISPLAY=':0'

and now I’m able to stream camera feed. Thank you

@Honey_Patouceul

Also note that the framerate property is not correct in the pipeline, if not just a typo when posting here you would correct it.

Yes it was a typo error while posting it here. I have fixed it now.