CMake Warning at cmake/OpenCVDownload.cmake:202 (message): IPPICV: Download failed: 28；“Timeout

• 具体错误：

CMake Warning at cmake/OpenCVDownload.cmake:202 (message):
  IPPICV: Download failed: 28;"Timeout was reached"

  For details please refer to the download log file:

  D:/OpenCV/opencv-4.5.5/build/CMakeDownloadLog.txt

Call Stack (most recent call first):
  3rdparty/ippicv/ippicv.cmake:37 (ocv_download)
  cmake/OpenCVFindIPP.cmake:259 (download_ippicv)
  cmake/OpenCVFindLibsPerf.cmake:12 (include)
  CMakeLists.txt:732 (include)

• 找到下载日志CMakeDownloadLog.txt

•  找到下载信息ippicv_2020_win_intel64_20191018_general.zip：

#do_unpack "ippicv_2020_win_intel64_20191018_general.zip" "879741a7946b814455eee6c6ffde2984" "https://raw.githubusercontent.com/opencv/opencv_3rdparty/a56b6ac6f030c312b2dce17430eef13aed9af274/ippicv/ippicv_2020_win_intel64_20191018_general.zip" "D:/OpenCV/opencv-4.5.5/build/3rdparty/ippicv"
#cmake_download "D:/OpenCV/opencv-4.5.5/.cache/ippicv/879741a7946b814455eee6c6ffde2984-ippicv_2020_win_intel64_20191018_general.zip" "https://raw.githubusercontent.com/opencv/opencv_3rdparty/a56b6ac6f030c312b2dce17430eef13aed9af274/ippicv/ippicv_2020_win_intel64_20191018_general.zip"

意思就是，下载https://ghproxy.com/https://raw.githubusercontent.com/opencv/opencv_3rdparty/a56b6ac6f030c312b2dce17430eef13aed9af274/ippicv/ippicv_2020_win_intel64_20191018_general.zip

到D:\OpenCV\opencv-4.5.5\.cache\ippicv\879741a7946b814455eee6c6ffde2984-ippicv_2020_win_intel64_20191018_general.zip

• 下载并复制文件

GitHub Proxy 代理加速

下载后， 复制到上述目录中，并改名。

• 同样办法，处理opencv_videoio_ffmpeg.dll

#do_copy "opencv_videoio_ffmpeg.dll" "eece4ec8304188117ffc7d5dfd0fc0ae" "https://raw.githubusercontent.com/opencv/opencv_3rdparty/4d348507d156ec797a88a887cfa7f9129a35afac/ffmpeg/opencv_videoio_ffmpeg.dll" "D:/OpenCV/opencv-4.5.5/build/3rdparty/ffmpeg"
#missing "D:/OpenCV/opencv-4.5.5/build/3rdparty/ffmpeg/opencv_videoio_ffmpeg.dll"
#check_md5 "D:/OpenCV/opencv-4.5.5/.cache/ffmpeg/eece4ec8304188117ffc7d5dfd0fc0ae-opencv_videoio_ffmpeg.dll"