在 Docker 中使用 OpenCV (Python) 访问网络摄像头？

Question

I'm trying to use Docker for one of our projects which uses OpenCV to process webcam feed (Python). But I can't seem to get access to the webcam within docker, here's the code which I use to test webcam access:

python -c "import cv2;print(cv2.VideoCapture(0).isOpened())"

And here's what I tried so far,

 docker run --device=/dev/video0 -it rec bash

 docker run --privileged --device=/dev/video0 -it rec bash

 sudo docker run --privileged --device=/dev/video0:/dev/video0 -it rec bash

All of these return False , what am I doing wrong?

Answer 1

The Dockerfile in the link you provided doesn't specify how opencv was installed, can you provide the Dockerfile you used? Or how you installed opencv?

VideoCapture(0) won't work if you install opencv via pip.

You're using --device=/dev/video0:/dev/video0 correctly.

Answer 2

Try to use this:

-v /dev/video0:/dev/video0

in place of

--device=/dev/video0 

and execute:

$ xhost + 

before docker run

Answer 3

The easisest way I found to have a dockerized OpenCV able to connect to your webcam is by using the following Dockerfile :

FROM ubuntu:20.04

ENV TERM=xterm
ENV DEBIAN_FRONTEND=noninteractive

RUN apt-get update && apt-get install -y --no-install-recommends \
    libopencv-dev \
    python3-opencv \
    && apt-get clean \
    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*

WORKDIR /app
ADD . /app

ENV PYTHONUNBUFFERED=1
ENV PYTHONPATH=/app

and then build it and run in this way :

docker build -t opencv-webcam .
docker run -it -v $PWD:/app/ --device=/dev/video0:/dev/video0 -v /tmp/.X11-unix:/tmp/.X11-unix -e DISPLAY=$DISPLAY opencv-webcam bash

and run the following script inside the container with python3 script.py :

import cv2


WINDOW_NAME = "Opencv Webcam"

def run():

    cv2.namedWindow(WINDOW_NAME)

    video_capture = cv2.VideoCapture(0)

    while True:
        ret, frame = video_capture.read()
        print(ret, frame.shape)

        cv2.imshow(WINDOW_NAME, frame)
        cv2.waitKey(1)

if __name__ == "__main__":
    run()

Answer 4

I ran into issues when using a non-privileged Dockerfile (ie with a USER line):

The container must be started with --user {UID} ; NOT --user {UID}:{GID} (same for user: line in docker-compose.yml, If the gid is set. weirdly this will not inherit the video group permission needed for access to the webcam files (/dev/video0 etc.), Also; the internal Dockerfile user must be added to the video group: add this after the USER line (and after installing sudo and adding the user to sudoers):

RUN sudo usermod -a -G video <InternalUsername>

Before you try theses steps: run everything in privileged mode to test if your problem lies really here.