学习OpenCV3：Cmake编译OpenCV时无法下载ffmpeg、xfeatures2d等文件

旧城等待， 2023-05-22 10:21 16阅读 0赞

--------------------

# 1. 错误描述 #

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:
    
      D:/opencv/bulid_mingw/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:22 (add_backend)
      cmake/OpenCVModule.cmake:312 (include)
      cmake/OpenCVModule.cmake:375 (_add_modules_1)
      modules/CMakeLists.txt:7 (ocv_glob_modules)

![无法下载opencv\_videoio\_ffmpeg.dll][opencv_videoio_ffmpeg.dll]

# 2. 分析 #

根据错误提示打开**D:/opencv/bulid\_mingw/CMakeDownloadLog.txt**。从中可发现出错的文件夹是**D:/opencv/sources/.cache**。在**D:/opencv/sources/.cache**中，凡是文件大小是0KB，都是无法下载并报错的。

#use_cache "D:/opencv/sources/.cache"
    #match_hash_in_cmake_cache "OCV_DOWNLOAD_ADE_HASH_3rdparty_ade_v0_1_1f_zip"
    #do_copy "opencv_videoio_ffmpeg.dll" "3b094c37d270a30f0b20a0bc8d3ecafb" "https://raw.githubusercontent.com/opencv/opencv_3rdparty/3d2e97081683265950316c65a52c2e8858ffba1b/ffmpeg/opencv_videoio_ffmpeg.dll" "D:/opencv/bulid_mingw/3rdparty/ffmpeg"
    #missing "D:/opencv/bulid_mingw/3rdparty/ffmpeg/opencv_videoio_ffmpeg.dll"
    #check_md5 "D:/opencv/sources/.cache/ffmpeg/3b094c37d270a30f0b20a0bc8d3ecafb-opencv_videoio_ffmpeg.dll"
    #mismatch_md5 "D:/opencv/sources/.cache/ffmpeg/3b094c37d270a30f0b20a0bc8d3ecafb-opencv_videoio_ffmpeg.dll" "d41d8cd98f00b204e9800998ecf8427e"
    #delete "D:/opencv/sources/.cache/ffmpeg/3b094c37d270a30f0b20a0bc8d3ecafb-opencv_videoio_ffmpeg.dll"
    #cmake_download "D:/opencv/sources/.cache/ffmpeg/3b094c37d270a30f0b20a0bc8d3ecafb-opencv_videoio_ffmpeg.dll" "https://raw.githubusercontent.com/opencv/opencv_3rdparty/3d2e97081683265950316c65a52c2e8858ffba1b/ffmpeg/opencv_videoio_ffmpeg.dll"
    #try 1
    # timeout on name lookup is not supported
    # getaddrinfo(3) failed for raw.githubusercontent.com:443
    # Couldn't resolve host 'raw.githubusercontent.com'
    # Closing connection 0
    #

![错误文件夹][format_png_pic_center]

![无法下载的文件][format_png_pic_center 1]

# 3. 解决方法 #

1.  打开[https://github.com/opencv/opencv\_3rdparty][https_github.com_opencv_opencv_3rdparty]，找到正确版本的ffmpeg并下载。若网速太慢或不能下载可以参考[学习OpenCV3：解决github下载速度慢的方法（码云）][OpenCV3_github]。

![opencv\_3rdparty][opencv_3rdparty]

![ffmpeg相关文件][ffmpeg]

1.  将下载的ffmpeg相关文件拷贝到**D:/opencv/sources/.cache**中。打开cmd，输入编译命令获取各个文件的MD5。当MD5相同时，用已下载的dll替换对应大小为0KB的dll文件，注意修改文件名，其格式是：MD5-文件名。

![拷贝下载的ffmpeg相关文件][ffmpeg 1]

cd /d D:\opencv\sources\.cache\ffmpeg
    certutil -hashfile ffmpeg_version.cmake MD5

![获取文件的MD5][MD5]

![替换后的ffmpeg相关文件][ffmpeg 2]

1.  同样的，对**D:/opencv/sources/.cache**大小为0KB的文件进行如上类似操作，最后重新点击**Configue**，编译便不会报此类错误了。

![正确编译结果][format_png_pic_center 2]

[opencv_videoio_ffmpeg.dll]: /images/20230521/9a726923b7c44f91b31228b0855cad03.png
[format_png_pic_center]: /images/20230521/43f73fc790654b478110272eaf8a250a.png
[format_png_pic_center 1]: /images/20230521/76b127494e8d494b9e4132220a7be7cc.png
[https_github.com_opencv_opencv_3rdparty]: https://github.com/opencv/opencv_3rdparty
[OpenCV3_github]: https://www.jianshu.com/p/9c27d60edc20
[opencv_3rdparty]: /images/20230521/ec5e4574d4104c04ab44628cf3a8b6b5.png
[ffmpeg]: /images/20230521/70e43d07fe354d24b915b5682224db01.png
[ffmpeg 1]: /images/20230521/6b1278dfd5294b5d963314e76c8dc9cf.png
[MD5]: /images/20230521/412f9cc781e049c584eef4501ab7d738.png
[ffmpeg 2]: /images/20230521/32550c0896a6477fbc464eb71ebe5412.png
[format_png_pic_center 2]: /images/20230521/88a7bbf3dd5545b6b9b08ff4595b1e4f.png