cv2.videocapture()失败，无法读取视频

原因：缺少ffmpeg的支持

解决：一般opencv3.3版本及以上支持ffmpeg，实验4.1.0成功

pip install opencv-python
pip install opencv-contrib-python

如果出现以下问题，则是由于libsm包为安装

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/site-packages/cv2/__init__.py", line 9, in <module>
    from .cv2 import *
ImportError: libSM.so.6: cannot open shared object file: No such file or directory