Read from linux web camera using OpenCV

Question

I'm trying to read raw video from web camera connected to my linux machine. I'm using OpenCV and l4v2 library (gstreamer). Here are some details on my camera:

root@blah:~$ v4l2-ctl -d /dev/video0 --list-formats
ioctl: VIDIOC_ENUM_FMT
        Index       : 0
        Type        : Video Capture
        Pixel Format: 'YUYV'
        Name        : YUV 4:2:2 (YUYV)

        Index       : 1
        Type        : Video Capture
        Pixel Format: ''
        Name        : e436eb7d-524f-11ce-9f53-0020af0

        Index       : 2
        Type        : Video Capture
        Pixel Format: 'RGB3' (emulated)
        Name        : RGB3

        Index       : 3
        Type        : Video Capture
        Pixel Format: 'BGR3' (emulated)
        Name        : BGR3

        Index       : 4
        Type        : Video Capture
        Pixel Format: 'YU12' (emulated)
        Name        : YU12

        Index       : 5
        Type        : Video Capture
        Pixel Format: 'YV12' (emulated)
        Name        : YV12

Here is my super simple code:

VideoCapture capture = VideoCapture(0);
if (!capture.isOpened()) {
      // Error in opening the video input
      cerr << "Unable to open video file for read: " << FLAGS_in_video << endl;
}
else {
  cout << "Opened video for read: " << FLAGS_in_video << endl;
}

And here is output and error I get:

Trying to open device 0 to read.
VIDEOIO ERROR: V4L/V4L2: VIDIOC_S_CROP
mmap: Invalid argument
Opened video for read: 0
Unable to stop the stream.: Bad file descriptor
munmap: Invalid argument
munmap: Invalid argument
munmap: Invalid argument
munmap: Invalid argument

I've built OpenCV with WITH_V4L and WITH_LIBV4L flags ON.

I'd appreciate any help or advise on how to fix it. Thank you.

Answer 1

Figured it out eventually - I had LP_PRELOAD which forced l4lib being loaded instead of l4v2.