ffmpeg avcodec_find_encoder_by_name failes to find encoder h264_nvenc - encoding

Question

When I run this command "ffmpeg -h encoder=h264_nvenc" in the terminal it gives me the following output
and I am able to use the encoder through the command line interface but it got a problem when I try to run from the following source code.
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
extern "C"
{
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/imgutils.h>
#include <libavutil/mathematics.h>
#include <libavutil/opt.h>
#include <libswscale/swscale.h>
#include <x264.h>
}
int main( int argc, char** argv )
{
const AVCodec *codec;
AVCodecContext *c= NULL;
av_register_all();
std::cout << "Loading codec" << std::endl;
// codec = avcodec_find_encoder_by_name( "libx264" ); // works
codec = avcodec_find_encoder_by_name( "h264_nvenc" );
// codec = avcodec_find_decoder_by_name( "h264_cuvid" );
if( !codec )
{
throw std::runtime_error( "Unable to find codec!" );
}
std::cout << "Allocating context" << std::endl;
return 0;
}

Answer 1

Here is a clear CMakeLists.txt file for this minimal example. Note that the libraries are not linked correctly if one uses link_directories( /usr/local/lib ), so I used add_library instead.
Furthermore, it seems not to be necessary to include the nvidia/cuda libraries to have access to nvenc codecs.
cmake_minimum_required(VERSION 2.8)
project( opencv-test )
include_directories(/usr/local/include)
add_executable( h264_nvenc
h264_nvenc.cpp
)
# link_directories( /usr/local/lib ) # does not work
add_library( avformat SHARED IMPORTED )
set_target_properties( avformat PROPERTIES IMPORTED_LOCATION /usr/local/lib/libavformat.so )
add_library( avutil SHARED IMPORTED )
set_target_properties( avutil PROPERTIES IMPORTED_LOCATION /usr/local/lib/libavutil.so )
add_library( avcodec SHARED IMPORTED )
set_target_properties( avcodec PROPERTIES IMPORTED_LOCATION /usr/local/lib/libavcodec.so )
add_library( swscale SHARED IMPORTED )
set_target_properties( swscale PROPERTIES IMPORTED_LOCATION /usr/local/lib/libswscale.so )
add_library( swresample SHARED IMPORTED )
set_target_properties( swresample PROPERTIES IMPORTED_LOCATION /usr/local/lib/libswresample.so )
target_link_libraries( h264_nvenc avformat swscale swresample avutil avcodec)

Answer 2

Your code works on my system (finds encoder). Make sure your ffmpeg source is up to date and configured and compiled with --enable-nvenc.
Update:
Can you please save above snipped as h264_nvenc.cpp and compile with this command:
g++ h264_nvenc.cpp -o h264_nvenc `PKG_CONFIG_PATH=/path/ffmpeg/lib/pkgconfig/ pkg-config --cflags libavformat libswscale libswresample libavutil libavcodec` `PKG_CONFIG_PATH=/path/ffmpeg/lib/pkgconfig/ pkg-config --libs libavformat libswscale libswresample libavutil libavcodec` -std=gnu++11
And than test the compiled file as ./h264_nvenc
You should then see:
Loading codec
Allocating context