cv2.videocapture 不适用于 Raspberry-pi

Question

How can i make the cv2.VideoCapture(0) recognize the USB camera of raspberry-pi.

def OnRecord(self, evt):
    capture = cv2.VideoCapture(0)
    if (not capture.isOpened()):
        print "Error"
# video recorder
    fourcc = cv2.cv.CV_FOURCC(*'XVID')  # cv2.VideoWriter_fourcc() does not exist
    video_writer = cv2.VideoWriter.open("output.mp4", fourcc, 20, (640, 480), True)

    # record video
    while (capture.isOpened()):
        ret, frame = capture.read()
        if ret==True:
            video_writer.write(frame)
            cv2.imshow('Video', frame)
        else:
            break

def OnCancel(self, evt):
    capture.release()
    video_writer.release()
    cv2.destroyAllWindows()

but it only prints Error.

So i guess capture is not opening. What might be the reason?

I tried this code from opencv documentation but doesn't worked out for me.

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

# Define the codec and create VideoWriter object
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc, 20.0, (640,480))

while(cap.isOpened()):
    ret, frame = cap.read()
    if ret==True:
        frame = cv2.flip(frame,0)

        # write the flipped frame
        out.write(frame)

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

# Release everything if job is finished
cap.release()
out.release()
cv2.destroyAllWindows()

Any help would be greatly appreciated.

Answer 1

为 linux 驱动程序加载正确的视频。

sudo modprobe bcm2835-v4l2

Answer 2

In my experience with CV2 replacing a webcam source on linux isn't always easy. How OpenCV works is it automatically draws from the systems default video source, which is known (usually) as video0. Unplug your usb webcam and go into a terminal and typing ls /dev/video*

Remember the number it says. Now plug in your USB webcam and type in ls /dev/video* again and look for any new /video, this is your USB webcam. Now type mv /dev/videoX videoY while X is the number of your USB webcam and Y the original number. This will replace your pi's default camera.

This isn't permanent as you will need to do this every time your pi starts up, an alternative to this is creating a bash file that runs on start up. Create a text file and copy the following into it.

#!/bin/bash
mv /dev/videoX videoY

(replace the X and Y of course)

and place that in /etc/init.d directory of your pi. Don't forget you may need to use
chmod 755 /etc/init.d/FILENAME.sh
to give it permission to run

Answer 3

Go to terminal and type lsusb and check whether the USB camera is recognized or not. If it is recognized then try to give different device ID such as 1 or 2 or 3 rather than 0.

Answer 4

looks Like you might have issue with codec, try using 'MJPG' codec instead of XVID. For more details have a look here

Answer 5

确保您使用的相机与 UVC 兼容，因为在基于 linux 的系统（如 raspi）上运行的 openCV 在使用非 UVC 相机时开始做一些愚蠢的事情。