Undefined reference, using FFMpeg-library (AvCodec) on Ubuntu, 64-bits system
I was (finally!!) referred to the solution in the FFMpeg-mailing list: http://ffmpeg.org/faq.html#I_0027m-using-FFmpeg-from-within-my-C_002b_002b-application-but-the-linker-complains-about-missing-symbols-which-seem-to-be-available_002e
Quote: "FFmpeg is a pure C project, so to use the libraries within your C++ application you need to explicitly state that you are using a C library. You can do this by encompassing your FFmpeg includes using extern "C"."
Anders Branderud
“How could it ever be to our purpose to rob another living being of his or her purpose?” ― Will Tuttle, The World Peace Diet: Eating for Spiritual Health and Social Harmony I love meeting friends and new people, being authentic, open and honest, exploring my self, long walks, blogging, reading, learning, taking photos... I don’t consume animal products, or use animals in other ways, because animals are harmed and killed in the production of meat, dairy, eggs, etc., and I don’t want to be part of this. I think we should treat everyone with love and compassion.
Updated on June 23, 2022Comments
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Anders Branderud about 2 years
I am running the example code of the latest FFMpeg-library. I have inserted the example code into the file
videofecencoder.c
:/* * 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 <stdlib.h> #include <stdio.h> #include <string.h> #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->bit_rate = 400000; /* resolution must be a multiple of two */ c->width = 352; c->height = 288; /* frames per second */ c->time_base= (AVRational){1,25}; c->gop_size = 10; /* emit one intra frame every ten frames */ c->max_b_frames=1; c->pix_fmt = PIX_FMT_YUV420P; if(codec_id == CODEC_ID_H264) av_opt_set(c->priv_data, "preset", "slow", 0); /* open it */ if (avcodec_open2(c, codec, NULL) < 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->data, picture->linesize, c->width, c->height, c->pix_fmt, 1); /* encode 1 second of video */ int nrOfFramesTotal = nrOfFramesPerSecond * nrOfSeconds; /* encode 1 second of video */ for(i=0;i < nrOfFramesTotal; i++) { fflush(stdout); /* prepare a dummy image */ /* Y */ for(y=0;y<c->height;y++) { for(x=0;x<c->width;x++) { picture->data[0][y * picture->linesize[0] + x] = x + y + i * 3; } } /* Cb and Cr */ for(y=0;y<c->height/2;y++) { for(x=0;x<c->width/2;x++) { picture->data[1][y * picture->linesize[1] + x] = 128 + y + i * 2; picture->data[2][y * picture->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->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 <= 1) { video_encode_example("/grb_1.mpg", CODEC_ID_MPEG1VIDEO); } else { filename = argv[1]; } return 0; }
When I run
gcc videofecencoder.cc -lavcodec
I get the following error messages:/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
The command
nm libavcodec.a | grep avcodec_find
results in: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
I also have another similar error with another library: Undefined reference despite linking in OpenFEC-library
My system: Ubuntu 11, 64-bits machine
My next step is to try to compile it on VirtualBox with Ubuntu 32 bits (running on a Windows-OS).
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Johannes Overmann about 11 yearsFFmpeg should really take care of this in the headers. C++ is a reality.