message: ffmpeg: update 3.4.6
  libvpx: 1.8.0
diff: -# Binaries branch name: ffmpeg/3.4_20181103
  -# Binaries were created for OpenCV: c6d2f0399a706028f476f3d08358ea787503020d
  -ocv_update(FFMPEG_BINARIES_COMMIT "fe71c0ad807fdc33c2178e48e488f1e9b177c39a")
  -ocv_update(FFMPEG_FILE_HASH_BIN32 "41b81bb9a50cabd4bea385f7b50a069a")
  -ocv_update(FFMPEG_FILE_HASH_BIN64 "a9ea7dbbc8e5afd08e00e223a831b578")
  +# Binaries branch name: ffmpeg/3.4_20190612
  +# Binaries were created for OpenCV: 1c661e754812d3423e8c15ccb9cdab57fc122c44
  +ocv_update(FFMPEG_BINARIES_COMMIT "d284fd09e76966e95f08e1ac3a1a28b227447501")
  +ocv_update(FFMPEG_FILE_HASH_BIN32 "a7032bf6cc1cb010dc055f352277792c")
  +ocv_update(FFMPEG_FILE_HASH_BIN64 "40d1a38b83a0413a3fcf9df1044fff2a")
  ocv_update(FFMPEG_FILE_HASH_CMAKE "3b90f67f4b429e77d3da36698cef700c")
  function(download_win_ffmpeg script_var)
  