delay of VideoCapture::read (python)

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I try to capture frame from IP camera by VideoCapture::read.

cap = cv2.VideoCapture(url)
while True:
    ret, frame = cap.read()

But, capture of 1st frame is delayed about 3 seconds, and subsequent behavior is different on the two PCs.
The version of OS(Windows10), python, OpenCV is same on two PCs. But hardware(model) is different.
The behavior on each PC is as follows.

• PC1 :
  Capture of 1st frame is delayed about 3 secondes.
  After that, the capture(display) looks like fast-forwarding, finally frame is captured(displayed) in real time.

• PC2 :
  Frame capture is delayed by fps as follows:
  

  3fps - about 2.5 seconds
  6fps - about 1.2 seconds
  9fps - about 0.7 seconds
  12fps - about 0.5 seconds
  15fps - about 0.5 seconds
  30fps - about 0.3 seconds

I want to make the behavior of PC2 the same as PC1.
I guess that the settings(like frame buffer) are different, but I don't know where I can set it.
Please help, if you know.