未定义的引用，在Ubuntu上使用FFMpeg库（AvCodec），64位系统 [英] Undefined reference, using FFMpeg-library (AvCodec) on Ubuntu, 64-bits system
问题描述
我正在运行最新的FFMpeg库的示例代码。
我已将示例代码插入到文件 videofecencoder.c 中：
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;
}
当我运行 gcc videofecencoder.cc -lavcodec 我得到以下错误消息：
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
命令 nm libavcodec.a | grep avcodec_find 结果：
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
我也有另外一个类似的错误与其他库：
的未定义的引用，尽管OpenFEC库中有链接
I also have another similar error with another library: Undefined reference despite linking in OpenFEC-library
我的系统：Ubuntu 11,64位机器
My system: Ubuntu 11, 64-bits machine
我的下一步是尝试使用Ubuntu 32位（在Windows操作系统上运行）上编译VirtualBox。
My next step is to try to compile it on VirtualBox with Ubuntu 32 bits (running on a Windows-OS).
推荐答案
我是（终于!!）提到FFMpeg邮件列表中的解决方案：
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
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
引用：FFmpeg是一个纯C项目，因此要使用C ++应用程序中的库，您需要明确声明您正在使用C库。你可以通过包含你的FFmpeg包括使用externC来做到这一点。
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"."
这篇关于未定义的引用，在Ubuntu上使用FFMpeg库（AvCodec），64位系统的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
