无法在opencv中保存视频

Question

I want to save my webcam video using opencv.

I wrote this code.

import numpy as np
import cv2

cap=cv2.VideoCapture(0)
#Define the codec
#FourCC code is passed as cv2.VideoWriter_fourcc('M','J','P','G')
#or cv2.VideoWriter_fourcc(*'MJPG') for MJPG.
fourcc = cv2.VideoWriter_fourcc(*'XVID')

#Define VideWrite object
#cv2.VideoWrite('arg1',arg2,arg3,(width,heigh))
#arg1:output file name
#arg2:Specify Fourcc code
#arg3: frames per seconds
#FourCC is a 4-byte code used to specify video codec
out=cv2.VideoWriter('SaveAVideo.avi',fourcc,20.0, (640,480))


while(cap.isOpened()):      

   ret,frame = cap.read()
   print('frame =',frame)
   print('ret = ',ret)
   if ret==True:
          frame =cv2.flip(frame,0)
          #Write the flipped frame
          out.write(frame)
          cv2.imshow('frame',frame)
          if cv2.waitKey(0) & 0xFF== ord('q'):
               break
   else:
          break
   print('after while loop')
# Release everything if job is finished
cap.release()
out.release()
cv2.destroyAllWindows()

The problem I am facing is that it is recording only black screen, although I have checked my webcam.

Answer 1

As I said in my comment, the solution is to change:

cv2.waitKey(0) 

to:

cv2.waitKey(another_value)

by example 1.

According to the docs the parameter that receives cv2.waitKey() indicates the delay that is given:

In your case it is necessary since saving the image in the video, also is always convenient since an image is given at 60Hz so Overcoming that frequency is unnecessary.