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"
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"
