FFMPEG Undefined Reference to 'avcodoec_open2' in C++ - c++

Question

I have an error when compiling one of my C++ programs after updating the FFMPEG library from 0.8 to 'ffmpeg version git-2012-04-12-277f20c'
The error I get when I make my program is as follows:
-------- begin --------
Linking: Analysing_Server
./source/Encoding_Thread.o: In function `CEncoding_Thread::do_work()':
/home/Analyser/source/Encoding_Thread.cpp:155: undefined reference to `avcodec_open2'
collect2: ld returned 1 exit status
make: *** [Analysing_Server] Error 1
The relevant lines of my Make file is similar to running g++ as below:
g++ test2.cpp -lavformat -lavcodec -lavutil -D__STDC_CONSTANT_MACROS
A stripped down version of my relevant CPP code that throws the error is:
#include <stdio.h>
#include <stdint.h>
#define LOG_OUT_STREAM_BUFF_SIZE 200000
extern "C" {
/* The ffmpeg library is completely written in C, so we need to tell the C++ compiler that so it links correctly. */
#include "stdint.h"
#include "libavcodec/avcodec.h"
#include "libavutil/mathematics.h"
#include "libswscale/swscale.h"
#include "libavfilter/avfilter.h"
int avcodec_open2(AVCodecContext *avctx, AVCodec *codec, AVDictionary **options);
int avcodec_encode_video2(AVCodecContext *avctx, AVPacket *avpkt, const AVFrame *frame, int *got_packet_ptr);
}
uint8_t m_outbuf[2][LOG_OUT_STREAM_BUFF_SIZE];
unsigned int m_out_size[2];
unsigned int m_OutBuffer_ID[2];
unsigned int m_Buffer_ID; /* This is just a uniqueish stamp we give to each buffer so we can tell when they change.. */
AVCodecContext * m_CodecContex;
AVCodec * m_codec;
struct SwsContext *m_img_convert_ctx;
unsigned char* m_DataBuff;
int Output_Width, Output_Height;
int Output_Bitrate;
int main(void) {
//New version of FFMPEG calls this in avcodec_register_all
//avcodec_init();
/* register all the codecs */
avcodec_register_all();
/* Initalise the encoder */
m_codec = avcodec_find_encoder(CODEC_ID_MP2);
if (!m_codec) {
printf("Encoding codec not found\n");
}
/* init the pointers.. */
m_CodecContex = NULL;
/* Default values.. */
Output_Width = 1600;
Output_Height = 1200;
Output_Bitrate = 600000;
/* Create/setup the Codec details.. */
//Changed to work with new FFMPEG
m_CodecContex = avcodec_alloc_context3(m_codec);
avcodec_get_context_defaults3(m_CodecContex, m_codec);
/* put sample parameters */
m_CodecContex->bit_rate = Output_Bitrate;
/* resolution must be a multiple of two */
m_CodecContex->width = Output_Width;
m_CodecContex->height = Output_Height;
/* frames per second */
m_CodecContex->time_base= (AVRational){1,25};
m_CodecContex->gop_size = 10; /* emit one intra frame every ten frames */
m_CodecContex->max_b_frames=1;
m_CodecContex->pix_fmt = PIX_FMT_YUV420P; /* must be YUV for encoding.. */
AVDictionary * RetunedAVDic;
/* open it */
//Changed to work with new FFMPEG
if (avcodec_open2(m_CodecContex, m_codec, &RetunedAVDic) < 0) {
printf("could not open codec");
}
}
Unfortunately the example under 'doc/examples/decoding_encoding.c' that comes with FFMPEG no longer works because all the functions that it uses are now depreciated. My code is based on the example code and worked fine with FFMPEG 0.8 but does not compile with the newest version of FFMPEG. I have changed some of the depreciated functions to their newer versions but it still doesn't compile.
Does anyone know why I am getting this error? or does anyone have a link to an example like 'doc/examples/decoding_encoding.c' using the newest version of FFMPEG?

Answer 1

The relevant lines of my Make file is similar to running g++ as below:
g++ test2.cpp -lavformat -lavcodec -lavutil -D__STDC_CONSTANT_MACROS
In programming, details matter. Your link command is not sufficiently similar to the above command, or it would have worked.
You probably are putting libraries in the wrong place on the link line. The order of sources and libraries matters.
Update:
If you put the code supplied above in a CPP file, then run g++ with the supplied options, it does not work. You will get the error "undefined reference to `avcodec_open2'".
No, I don't. I get a different error (since I don't have avcodec installed at all).
If the example command already fails for you, then you should provide the error it produced, not the error from some other command, so we wouldn't have to guess what that other command might have looked like.
The order of the libraries worked for FFMPEG version 0.8, why does it not work with the latest version?
Probably because you've installed the latest libavcodec54, but didn't install the latest libavcodec-dev.