前言

再此之前请确保你的环境变量是否配置，这是总共需要配置的环境变量
E:\cmake\bin
E:\OpenCv\opencv\build\x64\vc15\bin
F:\Qt\Tools\mingw730_64\bin
F:\Qt\5.12.4\mingw73_64\bin

问题一：

CMake Error: CMake was unable to find a build program corresponding to "MinGW Makefiles".  CMAKE_MAKE_PROGRAM is not set.  You probably need to select a different build tool.

解决：

双击，修改为mingw32-make.exe路径，重新configure就行了

问题二

CMake Error at cmake/OpenCVFindLibsGUI.cmake:18 (find_package):
  Could not find a package configuration file provided by "Qt5" with any of
  the following names:
    Qt5Config.cmake
    qt5-config.cmake
  Add the installation prefix of "Qt5" to CMAKE_PREFIX_PATH or set "Qt5_DIR"
  to a directory containing one of the above files.  If "Qt5" provides a
  separate development package or SDK, be sure it has been installed.
Call Stack (most recent call first):
  CMakeLists.txt:698 (include)

解决：

双击，修改为QT5路径即可，重新configure就行了

问题三：

CMake Warning at cmake/OpenCVDownload.cmake:202 (message):
  FFMPEG: Download failed: 6;"Couldn't resolve host name"
  For details please refer to the download log file:
  E:/OpenCv/opencv/opencv_bulid/CMakeDownloadLog.txt
Call Stack (most recent call first):
  3rdparty/ffmpeg/ffmpeg.cmake:20 (ocv_download)
  modules/videoio/cmake/detect_ffmpeg.cmake:14 (download_win_ffmpeg)
  modules/videoio/cmake/init.cmake:3 (include)
  modules/videoio/cmake/init.cmake:30 (add_backend)
  cmake/OpenCVModule.cmake:298 (include)
  cmake/OpenCVModule.cmake:361 (_add_modules_1)
  modules/CMakeLists.txt:7 (ocv_glob_modules)

解决：

打开CMakeDownloadLog.txt，会发现它说缺少

opencv_videoio_ffmpeg.dll

opencv_videoio_ffmpeg_64.dll

f8e65dbe4a3b4eedc0d2997e07c3f3fd-ffmpeg_version.cmake

让你去手动下载，并把下载地址贴了出来

https://raw.githubusercontent.com/opencv/opencv_3rdparty/6152e132572dfdaa32887eabeb7199bef49b14dc/ffmpeg/opencv_videoio_ffmpeg.dll

https://raw.githubusercontent.com/opencv/opencv_3rdparty/6152e132572dfdaa32887eabeb7199bef49b14dc/ffmpeg/opencv_videoio_ffmpeg_64.dll

https://raw.githubusercontent.com/opencv/opencv_3rdparty/6152e132572dfdaa32887eabeb7199bef49b14dc/ffmpeg/ffmpeg_version.cmake

前两个打开后就会自动下载，第三个网址，打开后会有一个网址，点击另存txt，改一下后缀就行，源文件上更改是不可以的
最后，把下载来的三个文件与之前文件替换一下即可，注意文件名称要一致

后记

有什么问题，欢迎探讨✨✨✨✨