从相机保存视频得到语法错误

Question

I am trying to save video from face cam in my dir.

I think I did everything correct. But I am getting syntax error in variable declaration.

Here's the error

Traceback (most recent call last): File "camera1.py", line 15, in cv2.imshow('frame', frame) cv2.error: OpenCV(4.2.0) /Users/travis/build/skvark/opencv-python/opencv/modules/highgui/src/window.cpp:376: error: (-215:Assertion failed) size.width>0 && size.height>0 in function 'imshow' ^

  1 from cv2 import *
  2 
  3 cap = cv2.VideoCapture()
  4 
  5 width = int(cap.get((cv2.CAP_PROP_FRAME_WIDTH))))
  6 height = int(cap.get((cv2.CAP_PROP_FRAME_HEIGHT)))
  7 
  8 writer = cv2.VideoWriter('mysupervideo.mp4', cv2.VideoWriter_fourcc(*'XVID'), 20, (width, height))
  9                                                                                                                  
 10 while True:
 11     ret, frame = cap.read()
 12     writer.write(frame)
 13     cv2.imshow('frame', frame)
 14 
 15     if cv2.waitKey(1) & 0xFF == ord('q'):
 16         break
 17 
 18 cap.release()
 19 writer.release()
 20 cv2.destroyAllWindows()                                                                                                                                                                                                                                                                        

Thanks for any help

Answer 1

There are multiple issues with the above code snippet.

1) There are extra parenthesis at the ends of line 5. It should be:

width = int(cap.get((cv2.CAP_PROP_FRAME_WIDTH)))

2) The error that you get here is because in lines 5 and 6 the values of width and height that you get is " 0 and 0". This is because in code above at line 3 you are creating "cap" object but its not capturing from camera hence height width is 0, 0. Instead modify the line to:

cap = cv2.VideoCapture(0)

This (0) indicates capture from camera. and hence you will get proper width and height.

3) I ran the following code snippet and it is working for me and it dumps a result video "mysupervideo.mp4" in present working directory:

from cv2 import *
cap = cv2.VideoCapture(0)
width = int(cap.get((cv2.CAP_PROP_FRAME_WIDTH)))
height = int(cap.get((cv2.CAP_PROP_FRAME_HEIGHT)))
print(width, height)
writer = cv2.VideoWriter('mysupervideo.mp4', cv2.VideoWriter_fourcc(*'XVID'), 20, (width, height))
while True:
    ret, frame = cap.read()
    writer.write(frame)
    cv2.imshow('frame', frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
cap.release()
writer.release()
cv2.destroyAllWindows()