無法在Python中使用OpenCV打開保存的視頻（Windows 10）

Question

代碼讀取train1.mov文件，顯示cv2.imshow('res', res)也保存名爲output.avi的文件。問題是，output.avi大約40 kb並且是空的。但cv2.imshow('res', res)顯示整個視頻。然後顯示以下錯誤。

Python代碼：

import numpy as np 
import cv2 

cap = cv2.VideoCapture('C:\\Users\\khan1\\Desktop\\python project\\color_threshold\\train1.mov') 

fourcc = cv2.VideoWriter_fourcc(*'XVID') 
out = cv2.VideoWriter('C:\\Users\\khan1\\Desktop\\python project\\color_threshold\\output.avi',fourcc, 20.0, (640,480)) 

while(cap.isOpened()): 
    _, frame = cap.read() 

    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV) 
    lower_green = np.array([40, 60, 60]) 
    upper_green = np.array([80, 255, 255]) 

    mask = cv2.inRange(hsv, lower_green, upper_green) 
    mask = cv2.GaussianBlur(mask, (7, 7), 0) 
    res = cv2.bitwise_and(frame, frame, mask=mask) 

    out.write(res) 

    cv2.namedWindow("res", cv2.WINDOW_NORMAL) 
    cv2.imshow('res', res) 
    if (cv2.waitKey(1) & 0xFF) == ord('q'): # Hit `q` to exit 
     break 

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

錯誤：

OpenCV Error: Assertion failed ((scn == 3 || scn == 4) && (depth == CV_8U || depth == CV_32F)) in cv::cvtColor, file C:\build\master_winpack-bindings-win32-vc14-static\opencv\modules\imgproc\src\color.cpp, line 9815 
Traceback (most recent call last): 
    File "C:/Users/khan1/Desktop/python project/color_threshold/savevid.py", line 19, in <module> 
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV) 
cv2.error: C:\build\master_winpack-bindings-win32-vc14-static\opencv\modules\imgproc\src\color.cpp:9815: error: (-215) (scn == 3 || scn == 4) && (depth == CV_8U || depth == CV_32F) in function cv::cvtColor 


Process finished with exit code 1 

我怎樣才能解決呢？

Answer 1

很明顯，你的錯誤發生在最後一幀;這就是爲什麼你的imshow仍然工作的原因，但它錯誤了，並沒有完成寫在while循環後發生的視頻。

cap.read()返回的第一個值是關於幀是否存在/被讀取的布爾值。所以你可以簡單地在代碼中插入一個if-else塊，以在幀被讀取時執行處理，如果沒有，則循環爲，這樣就可以完成寫入幀。

這應該修補代碼：

import numpy as np 
import cv2 

cap = cv2.VideoCapture('C:\\Users\\khan1\\Desktop\\python project\\color_threshold\\train1.mov') 

fourcc = cv2.VideoWriter_fourcc(*'XVID') 
out = cv2.VideoWriter('C:\\Users\\khan1\\Desktop\\python project\\color_threshold\\output.avi',fourcc, 20.0, (640,480)) 

while(cap.isOpened()): 
    ret, frame = cap.read() 
    if ret: 

     hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV) 
     lower_green = np.array([40, 60, 60]) 
     upper_green = np.array([80, 255, 255]) 

     mask = cv2.inRange(hsv, lower_green, upper_green) 
     mask = cv2.GaussianBlur(mask, (7, 7), 0) 
     res = cv2.bitwise_and(frame, frame, mask=mask) 

     out.write(res) 

     cv2.namedWindow("res", cv2.WINDOW_NORMAL) 
     cv2.imshow('res', res) 
     if (cv2.waitKey(1) & 0xFF) == ord('q'): # Hit `q` to exit 
      break 
    else: 
     break 

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

看到這個同樣的過程here的例子。