Why does ffmpeg cmake external project is not working - c++

Question

I'm trying to compile ffmpeg with h264 support as an external cmake project. But after compile it, I'm getting libavcodec reference errors.
The compile problem is occurring on Ubuntu 18.04 machine. I have installed all dependencies for ffmpeg and also libx264-dev.
Cmake external project
set( proj ffmpeg )
set( SHARED_FFMPEG )
set(BASIC
--extra-ldflags=-L/usr/local/lib
--extra-cflags=-I/usr/local/include
--enable-gpl
--enable-libx264)
option( FFMPEG_GPL "Use a GPL version of FFMPEG" OFF )
set(FFMPEG_INSTALL_DIR ${CMAKE_BINARY_DIR}/INSTALL )
ExternalProject_Add(${proj}
# Set up dirs
SOURCE_DIR ${CMAKE_BINARY_DIR}/${proj}
INSTALL_DIR ${FFMPEG_INSTALL_DIR}
# get the project
GIT_REPOSITORY "https://github.com/FFmpeg/FFmpeg.git"
GIT_TAG "n3.2.13"
# Build the project
BUILD_IN_SOURCE 1
# Configure step
# DO STH FOR THE ARCHITECTURE...
CONFIGURE_COMMAND <SOURCE_DIR>/configure --prefix=${FFMPEG_INSTALL_DIR} ${SHARED_FFMPEG} ${FFMPEG_GPL_FLAG} ${BASIC}
# BUILD_COMMAND ${CMAKE_MAKE_PROGRAM} -j${NProcessors}
)
# define the library suffix
if( SUPER_SHARED_LIBS )
if( APPLE )
set(LIBRARY_SUFFIX .dylib)
else( APPLE )
set(LIBRARY_SUFFIX .so)
endif( APPLE )
else( SUPER_SHARED_LIBS )
set(LIBRARY_SUFFIX .a)
endif( SUPER_SHARED_LIBS )
# ADD DIRECTORIES FOR DEPENDENCIES IN Main/CMakeLists.txt
set( FFMPEG_LIBRARYS libavcodec.a
libavformat.a
libavutil.a
libswscale.a
)
include_directories(${FFMPEG_INSTALL_DIR}/include)
set(FFMPEG_LIBRARY_DIRS ${FFMPEG_INSTALL_DIR}/lib/)
link_directories(${FFMPEG_LIBRARY_DIRS})
C++ Where I used the library
extern "C" {
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/mathematics.h"
#include "libswscale/swscale.h"
#define INBUF_SIZE 4096
#define AUDIO_INBUF_SIZE 20480
#define AUDIO_REFILL_THRESH 4096
}
...
fReceiveBuffer = new u_int8_t[DUMMY_SINK_RECEIVE_BUFFER_SIZE];
fReceiveBufferAV = new u_int8_t[DUMMY_SINK_RECEIVE_BUFFER_SIZE+4];
fReceiveBufferAV[0] = 0;
fReceiveBufferAV[1] = 0;
fReceiveBufferAV[2] = 0;
fReceiveBufferAV[3] = 1;
av_init_packet(&avpkt);
avpkt.flags |= AV_PKT_FLAG_KEY;
avpkt.pts = avpkt.dts = 0;
av_init_packet(&avpkt);
avpkt.flags |= AV_PKT_FLAG_KEY;
avpkt.pts = avpkt.dts = 0;
/* set end of buffer to 0 (this ensures that no overreading happens for damaged mpeg streams) */
memset(inbuf + INBUF_SIZE, 0, FF_INPUT_BUFFER_PADDING_SIZE);
//codec = avcodec_find_decoder(CODEC_ID_MPEG1VIDEO);
codec = avcodec_find_decoder(AV_CODEC_ID_H264);
...
Error:
[100%] Linking CXX executable ../../bin/awesom-o
/home/tiburcio/CLionProjects/awesom-o/cmake-build-debug/INSTALL/lib/libavcodec.a(libx264.o): In function `X264_frame':
/home/tiburcio/CLionProjects/awesom-o/cmake-build-debug/ffmpeg/libavcodec/libx264.c:280: undefined reference to `x264_picture_init'
/home/tiburcio/CLionProjects/awesom-o/cmake-build-debug/INSTALL/lib/libavcodec.a(libx264.o): In function `reconfig_encoder':
/home/tiburcio/CLionProjects/awesom-o/cmake-build-debug/ffmpeg/libavcodec/libx264.c:266: undefined reference to `x264_encoder_reconfig'
/home/tiburcio/CLionProjects/awesom-o/cmake-build-debug/INSTALL/lib/libavcodec.a(libx264.o): In function `X264_frame':
/home/tiburcio/CLionProjects/awesom-o/cmake-build-debug/ffmpeg/libavcodec/libx264.c:340: undefined reference to `x264_encoder_encode'