ffmpeg+cuda+opencv

为了让ffmpeg使用gpu进行解码，可以按以下步骤：

1 下载nvidia官网提供的ffmpeg，编译安装

https://developer.nvidia.com/ffmpeg

注意原来的选项上还需要添加上 --enable-shared

如果出现编译错误

ERROR: cuda requested, but not all dependencies are satisfied: ffnvcodec
参考：https://superuser.com/questions/1299064/error-cuvid-requested-but-not-all-dependencies-are-satisfied-cuda-ffnvcodec

git clone https://git.videolan.org/git/ffmpeg/nv-codec-headers.git
make
sudo make install

2 编译opencv

可以采用2.4.13.6

注意会出现报错

error: ‘CODEC_FLAG_GLOBAL_HEADER’ was not declared in this scope
解决办法参考  https://stackoverflow.com/questions/46884682/error-in-building-opencv-with-ffmpeg
即把以下三行拷贝到 cap_ffmpeg_impl.hpp 开头

#define AV_CODEC_FLAG_GLOBAL_HEADER (1 << 22)
#define CODEC_FLAG_GLOBAL_HEADER AV_CODEC_FLAG_GLOBAL_HEADER
#define AVFMT_RAWPICTURE 0x0020