libv4l2: error getting capabilities: Inappropriate ioctl for device

[shivSD]

I know this issue is related to opencv configuration while building. this is happening only on darknet/yolo. Highly appreciate if you can share the opencv configuration (cmake command and output)

Failed to query video capabilities: Inappropriate ioctl for device
libv4l2: error getting capabilities: Inappropriate ioctl for device
VIDEOIO ERROR: V4L: device ../../ Unable to query number of channels
Couldn't connect to webcam.

I have installed FFMPEG (from source), GStreamer & opencv with LIBV4L = ON.

-- Video I/O:
-- DC1394: YES (ver 2.2.4)
-- FFMPEG: YES
-- avcodec: YES (ver 56.60.100)
-- avformat: YES (ver 56.40.101)
-- avutil: YES (ver 54.31.100)
-- swscale: YES (ver 3.1.101)
-- avresample: YES (ver 2.1.0)
-- GStreamer: YES
-- v4l/v4l2: linux/videodev2.h

[prabindh]

Could you share the call sequence made, to open/read the webcam device ?

opencv4 configuration is as described in the post "Enabling OpenCV 4.1.0 pkg-config" at http://gpupowered.org/

[prabindh]

Just to confirm I ran the opencv webcam code in [https://answers.opencv.org/question/1/how-can-i-get-frames-from-my-webcam/], inside the arapaho test code, and it worked fine on the integrated webcam on the Dell laptop I have, ubuntu 18.04. I did not build ffmpeg from source, but installed as dependency per the link http://www.linuxfromscratch.org/blfs/view/svn/general/opencv.html.

[shivSD]

Thanks for your response @prabindh here is my code sequence

if(filename){
    printf("video file: %s\n", filename);
    cap = cvCaptureFromFile(filename);
}else{
    cap = cvCaptureFromCAM(cam_index);

    if(width){
        cvSetCaptureProperty(cap, CV_CAP_PROP_FRAME_WIDTH, width);
    }
    if(height){
        cvSetCaptureProperty(cap, CV_CAP_PROP_FRAME_HEIGHT, height);
    }
    if(fps){
        cvSetCaptureProperty(cap, CV_CAP_PROP_FPS, fps);
    }
}

if(!cap) error("Couldn't connect to webcam.\n");

with 3.4.5 opencv version on Ubuntu 16.04, we are getting following errror

Failed to query video capabilities: Inappropriate ioctl for device
libv4l2: error getting capabilities: Inappropriate ioctl for device
VIDEOIO ERROR: V4L: device ../../ Unable to query number of channels
Couldn't connect to webcam.

[prabindh]

Any reason to still stick with this API, instead of the "VideoCapture" class ? Have you tried out the snippet at - https://answers.opencv.org/question/1/how-can-i-get-frames-from-my-webcam/. If that also does not work, do try with different camera. I am also puzzled why this should happen only with yolo. Are you able to run it standalone ?

[prabindh]

Any update on this ?