VIDEOIO ERROR: V4L: can't find camera device

Question

I am using ubuntu16.04 and trying to run opencv script. when i use:

video_capture = cv2.VideoCapture(-1)

it gives me error VIDEOIO ERROR: V4L: can't find camera device No video window opens But when i run

video_capture = cv2.VideoCapture('test.jpg')

It opens window shows the picture and close the window. Please tell me why it is not streaming video directly from camera.

Solution

The suggestion api55 gave in his comment

video_capture = cv2.VideoCapture(0)

is what I would try first.

Generally, you can list the available cameras with ls /dev/video* or v4l2-ctl --list-devices. Here sample output:

NZXT-U:rt-trx> v4l2-ctl --list-devices
Microsoft® LifeCam Cinema(TM): (usb-0000:00:14.0-1):
    /dev/video1

Microsoft® LifeCam Cinema(TM): (usb-0000:00:1a.0-1.3):
    /dev/video0

/dev/video0 corresponds to device id 0, etc.

PS: v4l2-ctl is quite useful for solving camera issues and can do much more than --list-devices. I installed it via packagev4l-utils on a 16.04 machine.

Comments

[Neeraj Sharma]

Thank you very much Ulrich for your answer. I did sudo apt-get install cheese and it started working.

[Ulrich Stern]

@NeerajSharma, I took a quick look at the OpenCV source code, and VideoCapture does support negative device numbers (at least for cap_v4l.cpp), even though this is not in the docs! You could answer your own question. If you are not interested, I will edit my answer.

[Neeraj Sharma]

Yes i tried with -1 and it worked. Thanks for your support Ulrich.