OpenCv error can't open camera through video capture

Question

I was using my cam through opencv and suddenly after restarting I ran my code it shows below error:

[ WARN:0] global /io/opencv/modules/videoio/src/cap_v4l.cpp (802) open VIDEOIO ERROR: V4L: can't open camera by index 0
Traceback (most recent call last):
  File "test.py", line 20, in <module>
    retval, buffer_img = cv2.imencode('.jpg', frame)
cv2.error: OpenCV(4.1.2) /io/opencv/modules/imgcodecs/src/loadsave.cpp:877: error: (-215:Assertion failed) !image.empty() in function 'imencode'

cap = cv2.VideoCapture(0)  # here it throws an error


import json
while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()

    retval, buffer_img = cv2.imencode('.jpg', frame)

    resdata = base64.b64encode(buffer_img)

    resdata = "data:image/png;base64,"+ str(resdata.decode("utf-8"))
    PARAMS = {'image': resdata}

    # Our operations on the frame come here
    #gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # Display the resulting frame
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()

I also tried with cap = cv2.VideoCapture(1) but then it shows can't find camera

How can I fix this issue?

score 23 · Answer 1 · edited Jul 26 '20 at 19:47

23

I got the same error. Try changing 0 to -1

cap = cv2.VideoCapture(-1)

This solved the issue.

edited Jul 26 '20 at 19:47

Matt Ke

3,599
12
30
49

answered Jul 26 '20 at 19:22

abey

239
2
3

your got error cause -1 index. -1 index meaning last element of list. i recommend you. you may use 0 if you have webcam. – MD. Saiful Islam Nov 17 '20 at 03:12

score 17 · Answer 2 · answered May 15 '20 at 10:58

I got the same problem when I created more than one instance of the cv2.VideoCapture(0). So check if your code contains multiple initializations or sections which call cv2.VideoCapture(0) more than once. I was facing this problem while running the flask server in debug mode because it called cv2.VideoCapture(0) twice.

import cv2
cap = cv2.VideoCapture(0)
cap2 = cv2.VideoCapture(0)
while True:

    ret, frame = cap.read()
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

Error:

python3 debugCamera.py 
[ WARN:0] global /io/opencv/modules/videoio/src/cap_v4l.cpp (887) open VIDEOIO(V4L2:/dev/video0): can't open camera by index

You try to open a camera two times. When a hardware ingress a work then it don't allow outer command at same time . — MD. Saiful Islam, Nov 17 '20 at 03:04

score 14 · Answer 3 · edited Nov 04 '20 at 23:53

14

Most likely a permission issue on /dev/video0.

Check if you are part of "video" group.
id -a

if you don't see video in your group list add sudo usermod -a -G video

for Ubuntu users:(20.04)
sudo usermod -a -G video $LOGNAME

Logout and log back in and try it.

edited Nov 04 '20 at 23:53

Pranav Durai

9
4

answered Oct 22 '20 at 20:48

Mazhai

141
1
2

It worked for me to run a X application inside docker container. I have also needed to install v4l-utils. Just like [this tutorial](https://medium.com/@petehouston/install-v4l-utils-on-debian-based-distros-d4f5c2fdcf61). – Diego Medeiros Aug 20 '21 at 21:15
I am using a rdp user for the xrdp server on the raspberry 4, and giving permissions was the solution, Thanks. For the pi, must be sudo usermod -a -G video $LOGNAME – Jaume Dec 27 '22 at 00:07

veradeus · Answer 4 · 2020-03-23T12:16:17.487

4

I had the same problem, Just change 0 to 1,then to -1 and back again to 0. Don't know why this worked for me.

edited Mar 23 '20 at 12:16

answered Mar 23 '20 at 11:41

veradeus

41
4

1

it makes no sense whatsoever , but it worked for me too – Kabir Lovero Sep 20 '21 at 12:13

score 4 · Answer 5 · edited Feb 18 '21 at 17:32

4

I've encountered the same issue and attempted several methods like cv2.VideoCapture(-1) or cv2.VideoCapture(1) but without much success.

I succeeded after reading this article and disabling debug-mode

edited Feb 18 '21 at 17:32

Adalcar

1,458
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answered Feb 18 '21 at 15:14

chilin

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There is nothing about disabling debug-mode in the article. Looks like a spam. – Leonid Mednikov Jul 05 '23 at 11:52
@LeonidMednikov I think the author remove some information from his article, I solved the issue by this way at that time. If this solution is obsolete you should correct the answer, downvoting cannot help other people. – chilin Jul 09 '23 at 07:09

score 4 · Answer 6 · answered Feb 08 '22 at 09:59

4

I found a solution in https://github.com/opencv/opencv/issues/19527 where the video capture is inside the function instead of outside. That worked for me (ubuntu)

def frame_generation():

camera = cv2.VideoCapture(0) #resolved, correct position

while(True):

answered Feb 08 '22 at 09:59

Diego

43
4

I don't know why but it works for me, no other solution worked – Yhozen Apr 11 '22 at 16:00
Didn't solve this problem for me, but this is much neater and more logical than leaving it within the loop. So I've done it anyway, – Hugh Barnard Feb 01 '23 at 13:09

score 2 · Answer 7 · answered Dec 17 '19 at 09:43

2

I will not go to that part What you are trying to do, here is just a block of code that can open your camera every time you run it,

python: 3.7.3

OpenCV: 4.1.0

import cv2
cap = cv2.VideoCapture(0)
while True:

    ret, frame = cap.read()
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

answered Dec 17 '19 at 09:43

Sohel Reza

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1
6
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3

cap = cv2.VideoCapture(0), its not working,its giving me the error I mentioned in the beginning – Nabeel Ayub Dec 17 '19 at 09:57
what kind of camera are you using? Laptop default camera(0), external camera(1-....), just change the value 0-... and see what happen. – Sohel Reza Dec 17 '19 at 10:01
I have used (-1) it gives can't find camera device – Nabeel Ayub Dec 17 '19 at 10:01
1

just change it 0 to 1 or 2 or 3 , if it is not work then problem maybe you python or openCV version. you can reinstall it and see what happen, just a quick suggestion – Sohel Reza Dec 17 '19 at 10:04
1

did all sort of things still can't fix,I think there is ubuntu compatibility issue otherwise it should run. – Nabeel Ayub Dec 17 '19 at 10:13

score 2 · Answer 8 · answered Sep 01 '21 at 18:50

I also had the same problem. Just changed it to 1 and it was perfectly working. I guess it's related to the number of camera devices you have used.

For example, I guess I have Iruin external camera as my first option which I didn't connect this time.

Here is the error and corrected code.

global /tmp/pip-req-build-f51eratu/opencv/modules/videoio/src/cap_v4l.cpp (890) open VIDEOIO(V4L2:/dev/video0): can't open camera by index

Code to change:

vid = cv2.VideoCapture(1)

score 2 · Answer 9 · answered Dec 09 '21 at 14:39

The OP appears to be operating on a Raspberry PI. Raspberry is moving to a new system to manage cameras, so when the user upgrades the OS via sudo apt-get upgrade the camera system gets the new library and the legacy camera system is disabled. To enable the legacy camera system again, try

sudo raspi-config

Then select

3 Interface Options    Configure connections to peripherals

then select

I1 Legacy Camera Enable/disable legacy camera support

and follow the directions to enable and then reboot.

Of course, this patch will only work for so long, as the legacy system has been deprecated.

score 1 · Answer 10 · answered Feb 16 '21 at 01:06

1

In my case, I just reconnected cam to the usb port, and then it was solved! I think this error is caused by closing the window in the wrong way. Please check if there is any exception on the terminal right after closing the window.

answered Feb 16 '21 at 01:06

129lovely

19
1

I don't think answers to software problems should include hardware/manual solutions. I might be as helpful as "restart your program" when you stumble upon an error somewhere – quqa123 Apr 14 '23 at 11:29

score 1 · Answer 11 · answered Dec 08 '21 at 21:09

1

I've also had this problem on Ubuntu

I've solved this by these comands

sudo adduser username video sudo usermod -a -G video username

username - it is the name of your device

than write

id -a

and copy index from ()

for me it is 1000

so than just write:

camera = cv2.VideoCapture(1000)

answered Dec 08 '21 at 21:09

TOPworkOUT

19
1

Welcome to Stack Overflow. Are you sure this answers the question at the top of the page? It doesn't appear to be related. Please read [answer]. – ChrisGPT was on strike Dec 08 '21 at 21:12

score 1 · Answer 12 · answered Aug 04 '22 at 18:45

1

Tried every anwser but only changing camera id from -1 to 1 and then back to 0 worked.

answered Aug 04 '22 at 18:45

X.Liu

11
1

score 1 · Answer 13 · edited Oct 24 '22 at 11:15

1

video = cv2.VideoCapture(0,cv2.CAP_DSHOW)

This worked for me.

edited Oct 24 '22 at 11:15

The Thonnu

3,578
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8
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answered Oct 20 '22 at 07:46

Anamika Gupta

31
4

score 0 · Answer 14 · answered Sep 20 '21 at 17:07

0

For Linux, make sure OpenCV is built using the WITH_V4L (with video for linux).

answered Sep 20 '21 at 17:07

Gardinal

74
6

score 0 · Answer 15 · answered Aug 26 '22 at 11:24

0

I have do everytime after restart or unplug usb camera and replug

chmod 777 /dev/video0

answered Aug 26 '22 at 11:24

Du Nguyễn Phan

69
8

score 0 · Answer 16 · answered Oct 21 '22 at 17:10

Don't know if this is still an issue. In my case, I was getting the same error until I unplugged and plugged the usb camera. Even if I reboot, the error happened.

It's similar to someone said: my camera was already been captured. The problem is that it was not used by my script, so it was hard to identify.

A few days before the issue, I installed the motion library, but just to test something and I didn't use it anymore. The motion starts at boot, so the camera was being captured by the service. That's why only the unplug-plug worked.

I uninstalled the library, and the error was gone.

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). — user11717481, Oct 24 '22 at 13:41

score -1 · Answer 17 · answered Jan 03 '21 at 11:43

-1

This issue is due to the interruption. Try to end the execution with the key 'q' for example, don't close the window suddenly.

I solved the same issue by opening terminal again and execute the same script again.

answered Jan 03 '21 at 11:43

Amine Sehaba

122
6

OpenCv error can't open camera through video capture

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