cv.VideoCapture遇到的问题记录

1、视频播放不出来

import numpy as np
import cv2 as cv
cap = cv.VideoCapture('opencv\111.mp4')
while(cap.isOpened()):
    ret, frame = cap.read()
    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
    cv.imshow('frame',gray)
    if cv.waitKey(1) & 0xFF == ord('q'):
        break
cap.release()
cv.destroyAllWindows()

路径修改为’opencv\111.mp4’，成功

2、

import numpy as np
import cv2 as cv
cap = cv.VideoCapture('opencv\\111.mp4')
while(cap.isOpened()):
    ret, frame = cap.read()
    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
    cv.imshow('frame',gray)
    if cv.waitKey(1) & 0xFF == ord('q'):
        break
cap.release()
cv.destroyAllWindows()

视屏可播放，播放到最后一帧出错

发生异常: error
OpenCV(4.1.0) C:\projects\opencv-python\opencv\modules\imgproc\src\color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'
  File "C:\Users\Desktop\opencv4\opencv\2.2.2play video.py", line 18, in <module>
    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)

修改为

import numpy as np
import cv2 as cv
cap = cv.VideoCapture('opencv\\111.mp4')
while(cap.isOpened()):
    ret, frame = cap.read()
    if ret:   
        gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
        cv.imshow('frame',gray)
        if cv.waitKey(25) & 0xFF == ord('q'):
            break    
    else:
        break
cap.release()
cv.destroyAllWindows()