get（cv2.CAP_PROP_FOURCC）使用openCV和python返回错误

Question

I have to read a local .avi files and make it shaw on a window.Here is my code:

import os,cv2
user=os.path.expanduser('~')
capture=cv2.VideoCapture(str(user)+"/Downloads/vehicle/Sunny/april21.avi")
if(capture.isOpened()):
    print "Open"
else:
    print "Fail to open!"
fps=capture.get(cv2.CAP_PROP_FPS)
fourcc=capture.get(cv2.CAP_PROP_FOURCC)
print fourcc#why fourcc is return 0.0?
print "fps:%d"%fps
size=(int(capture.get(cv2.CAP_PROP_FRAME_WIDTH))/2,
    (int)(capture.get(cv2.CAP_PROP_FRAME_HEIGHT))/2
    )
isStop=1
while isStop:
    grabbed,frame=capture.read()#frame is None
    cv2.namedWindow("window")
    img=cv2.resize(frame,size,interpolation=cv2.INTER_CUBIC)
    cv2.imshow("window",img)
    c=0xFF&cv2.waitKey(1)
    if c ==27:
        isStop=False
        cv2.destroyAllWindows()

But now the result is :

Open
0.0
fps:29
OpenCV Error: Assertion failed (ssize.area() > 0) in resize, file /Users/tom/opencv-3.1.0/modules/imgproc/src/imgwarp.cpp, line 3229
Traceback (most recent call last):
  File "/Users/tom/Documents/readVideo.py", line 20, in <module>
    img=cv2.resize(frame,size,interpolation=cv2.INTER_CUBIC)
cv2.error: /Users/tom/opencv-3.1.0/modules/imgproc/src/imgwarp.cpp:3229: error: (-215) ssize.area() > 0 in function resize

The only thing I am sure is these codes are right,cause I have created a .avi files through cv2.VideoWriter and it can be read and shown on a window. Thanks for answer.

Answer 1

Much likely the data type being returned by OpenCV is a double (floating point) whose arbitrary content (the FOURCC code) is invalid (not IEEE compliant).

I don't know Python but the following C/C++ snippet do the work:

union {
    char    c[5];
    int     i;
} myfourcc;
myfourcc.i = capture.get(CV_CAP_PROP_FOURCC);
myfourcc.c[4] = '\0';
std::cout << "4cc:" << myfourcc.c << std::endl;

I guess Python has a more idiomatic way that just the ctypes. Just my pennies.