Opencv 3.4.1.15 with python 3.6.8 not able to extract all video frames from latest version 15.3.1 IOS video

Expected behaviour

Getting all 300 frames from the video
Write here how did you expect the library to function.
cv2.VideoCapture(videopath)
should extract all the frames from the video

Actual behaviour

vs = cv2.VideoCapture(videopath)
while True:
_,frame = vs.read()

The above code is not reading all frames

Write here what went wrong.
Expected to read all frames, but just after 30 frames, I am getting a NULL frame.

Steps to reproduce

• example code
• operating system
• architecture (e.g. x86)
• OpenCV-python version

Issue submission checklist

• This is not a generic OpenCV usage question (looking for help for coding, other usage questions, homework etc.)
• I have read the README of this repository and understand that this repository provides only an automated build toolchain for OpenCV Python packages (there is no actual OpenCV code here)
• The issue is related to the build scripts in this repository, to the pre-built binaries or is a feature request (such as "please enable this additional dependency")
• I'm using the latest version of opencv-python
  No I am using OpenCV3.4.1.15 with python 3.6.8

No repository files, tests, operating system, architecture, or reproducible video are provided. First verify the reported behavior with the stated OpenCV and Python versions, then determine whether it belongs in this build-toolchain repository or the upstream OpenCV project; done requires a complete, repository-relevant reproduction and a confirmed target for the fix.