title: Undefined reference, using FFMpeg-library (AvCodec) on Ubuntu, 64-bits system
body: <p>I am running the example code of the latest FFMpeg-library.
  I have inserted the example code into the file <code>videofecencoder.c</code>:</p>
  
  <pre><code>/*
  * copyright (c) 2001 Fabrice Bellard
  *
  * This file is part of Libav.
  *
  * Libav is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * Libav is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with Libav; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
  #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
  
  
  #include &lt;stdlib.h&gt;
  #include &lt;stdio.h&gt;
  #include &lt;string.h&gt;
  
  #ifdef HAVE_AV_CONFIG_H
  #undef HAVE_AV_CONFIG_H
  #endif
  
  #include "libavutil/imgutils.h"
  #include "libavutil/opt.h"
  #include "libavcodec/avcodec.h"
  #include "libavutil/mathematics.h"
  #include "libavutil/samplefmt.h"
  
  #define INBUF_SIZE 4096
  #define AUDIO_INBUF_SIZE 20480
  #define AUDIO_REFILL_THRESH 4096
  
  /*
  * Video encoding example
  */
  static void video_encode_example(const char *filename, int codec_id)
  {
     AVCodec *codec;
     AVCodecContext *c= NULL;
     int i, out_size, size, x, y, outbuf_size;
     FILE *f;
     AVFrame *picture;
     uint8_t *outbuf;
     int nrOfFramesPerSecond  =25;
     int nrOfSeconds =1;
  
  
     printf("Video encoding\n");
  
     /* find the mpeg1 video encoder */
     codec = avcodec_find_encoder((CodecID) codec_id);
     if (!codec) {
         fprintf(stderr, "codec not found\n");
         exit(1);
     }
  
     c = avcodec_alloc_context3(codec);
     picture= avcodec_alloc_frame();
  
     /* put sample parameters */
     c-&gt;bit_rate = 400000;
     /* resolution must be a multiple of two */
     c-&gt;width = 352;
     c-&gt;height = 288;
     /* frames per second */
     c-&gt;time_base= (AVRational){1,25};
     c-&gt;gop_size = 10; /* emit one intra frame every ten frames */
     c-&gt;max_b_frames=1;
     c-&gt;pix_fmt = PIX_FMT_YUV420P;
  
     if(codec_id == CODEC_ID_H264)
         av_opt_set(c-&gt;priv_data, "preset", "slow", 0);
  
     /* open it */
     if (avcodec_open2(c, codec, NULL) &lt; 0) {
         fprintf(stderr, "could not open codec\n");
         exit(1);
     }
  
     f = fopen(filename, "wb");
     if (!f) {
         fprintf(stderr, "could not open %s\n", filename);
         exit(1);
     }
  
     /* alloc image and output buffer */
     outbuf_size = 100000;
     outbuf = (uint8_t*) malloc(outbuf_size);
  
     /* the image can be allocated by any means and av_image_alloc() is
      * just the most convenient way if av_malloc() is to be used */
     av_image_alloc(picture-&gt;data, picture-&gt;linesize,
                    c-&gt;width, c-&gt;height, c-&gt;pix_fmt, 1);
  
     /* encode 1 second of video */
     int nrOfFramesTotal = nrOfFramesPerSecond * nrOfSeconds;
  
     /* encode 1 second of video */
     for(i=0;i &lt; nrOfFramesTotal; i++) {
         fflush(stdout);
         /* prepare a dummy image */
         /* Y */
         for(y=0;y&lt;c-&gt;height;y++) {
             for(x=0;x&lt;c-&gt;width;x++) {
                 picture-&gt;data[0][y * picture-&gt;linesize[0] + x] = x + y + i * 3;
             }
         }
  
         /* Cb and Cr */
         for(y=0;y&lt;c-&gt;height/2;y++) {
             for(x=0;x&lt;c-&gt;width/2;x++) {
                 picture-&gt;data[1][y * picture-&gt;linesize[1] + x] = 128 + y + i * 2;
                 picture-&gt;data[2][y * picture-&gt;linesize[2] + x] = 64 + x + i * 5;
             }
         }
  
         /* encode the image */
         out_size = avcodec_encode_video(c, outbuf, outbuf_size, picture);
         printf("encoding frame %3d (size=%5d)\n", i, out_size);
         fwrite(outbuf, 1, out_size, f);
     }
  
     /* get the delayed frames */
     for(; out_size; i++) {
         fflush(stdout);
  
         out_size = avcodec_encode_video(c, outbuf, outbuf_size, NULL);
         printf("write frame %3d (size=%5d)\n", i, out_size);
         fwrite(outbuf, 1, out_size, f);
     }
  
     /* add sequence end code to have a real mpeg file */
     outbuf[0] = 0x00;
     outbuf[1] = 0x00;
     outbuf[2] = 0x01;
     outbuf[3] = 0xb7;
     fwrite(outbuf, 1, 4, f);
     fclose(f);
     free(outbuf);
  
     avcodec_close(c);
     av_free(c);
     av_free(picture-&gt;data[0]);
     av_free(picture);
     printf("\n");
  }
  
  int main(int argc, char **argv)
  {
     const char *filename;
  
     /* register all the codecs */
     avcodec_register_all();
  
     if (argc &lt;= 1) {
  
         video_encode_example("/grb_1.mpg", CODEC_ID_MPEG1VIDEO);
     } else {
         filename = argv[1];
     }
  
  
     return 0;
  }
  </code></pre>
  
  <p>When I run <code>gcc videofecencoder.cc -lavcodec</code> I get the following error messages:</p>
  
  <pre><code>/tmp/ccJg8IDy.o: In function `video_encode_example(char const*, int)':
  videofecencoder.cc:(.text+0x35): undefined reference to `avcodec_find_encoder(CodecID)'
  videofecencoder.cc:(.text+0x74): undefined reference to `avcodec_alloc_context3(AVCodec*)'
  videofecencoder.cc:(.text+0x7d): undefined reference to `avcodec_alloc_frame()'
  videofecencoder.cc:(.text+0x113): undefined reference to `av_opt_set(void*, char const*, char const*, int)'
  videofecencoder.cc:(.text+0x12b): undefined reference to `avcodec_open2(AVCodecContext*, AVCodec*, AVDictionary**)'
  videofecencoder.cc:(.text+0x1f0): undefined reference to `av_image_alloc(unsigned char**, int*, int, int, PixelFormat, int)'
  videofecencoder.cc:(.text+0x35c): undefined reference to `avcodec_encode_video(AVCodecContext*, unsigned char*, int, AVFrame const*)'
  videofecencoder.cc:(.text+0x3cf): undefined reference to `avcodec_encode_video(AVCodecContext*, unsigned char*, int, AVFrame const*)'
  videofecencoder.cc:(.text+0x47c): undefined reference to `avcodec_close(AVCodecContext*)'
  videofecencoder.cc:(.text+0x488): undefined reference to `av_free(void*)'
  videofecencoder.cc:(.text+0x497): undefined reference to `av_free(void*)'
  videofecencoder.cc:(.text+0x4a3): undefined reference to `av_free(void*)'
  /tmp/ccJg8IDy.o: In function `main':
  videofecencoder.cc:(.text+0x4c3): undefined reference to `avcodec_register_all()'
  collect2: ld returnerade avslutningsstatus 1
  </code></pre>
  
  <p>The command <code>nm libavcodec.a | grep avcodec_find</code> results in:</p>
  
  <pre><code>00000000000008e0 T avcodec_find_best_pix_fmt
  0000000000000740 T avcodec_find_best_pix_fmt2
                   U avcodec_find_encoder
  0000000000002ca0 T avcodec_find_decoder
  0000000000002cf0 T avcodec_find_decoder_by_name
  0000000000002bd0 T avcodec_find_encoder
  0000000000002c30 T avcodec_find_encoder_by_name
  </code></pre>
  
  <p>I also have another similar error with another library:
  <a href="https://stackoverflow.com/questions/9700373/undefined-reference-despite-linking-in-openfec-library">Undefined reference despite linking in OpenFEC-library</a></p>
  
  <p>My system: Ubuntu 11, 64-bits machine</p>
  
  <p>My next step is to try to compile it on VirtualBox with Ubuntu 32 bits (running on a Windows-OS).</p>