ffmpeg库使用及其错误解决

ffmpeg库使用及其错误解决

1.首先，需要弄明白Linux下动态库和静态库基础知识，这个网上自行搜索；

(1)linux动态库和静态库工作原理；

(2)如何用制作linux动态库和静态库；

(3)如何引用linux动态库和静态库；

2.ffmpeg动态库和静态库选项设定及编译

动态库 --enable-shared

./configure --prefix="ffmpeg-release-3.0/ffmpeg_build" --bindir="ffmpeg-release-3.0/ffmpeg_build/bin" --enable-shared --enable-gpl --extra-cflags="-I/ffmpeg-release-3.0/include" --extra-ldflags="-L/ffmpeg-release-3.0/ffmpeg_build/lib"
make V=1

make install V=1

静态库 --enable-static

./configure --prefix="ffmpeg-release-3.0/ffmpeg_build" --bindir="ffmpeg-release-3.0/ffmpeg_build/bin" --enable-static --enable-gpl --extra-cflags="-I/ffmpeg-release-3.0/include" --extra-ldflags="-L/ffmpeg-release-3.0/ffmpeg_build/lib"
make V=1

make install V=1

编译完成后：

ffmpeg_build/lib$ ls -l --block-size=m
total 200M
-rw-r--r-- 1 wr wr 128M Sep 18 10:42 libavcodec.a
-rw-r--r-- 1 wr wr   2M Sep 18 10:42 libavdevice.a
-rw-r--r-- 1 wr wr  19M Sep 18 10:42 libavfilter.a
-rw-r--r-- 1 wr wr  43M Sep 18 10:42 libavformat.a
-rw-r--r-- 1 wr wr   3M Sep 18 10:42 libavutil.a
-rw-r--r-- 1 wr wr   1M Sep 18 10:42 libpostproc.a
-rw-r--r-- 1 wr wr   1M Sep 18 10:42 libswresample.a
-rw-r--r-- 1 wr wr   7M Sep 18 10:42 libswscale.a
drwxr-xr-x 2 wr wr   1M Sep 18 10:42 pkgconfig

3.单个ffmpeg库使用：建议用ffmpeg动态库，静态库太大了，100多M，由于我编译的是静态库，那就以静态库示例；

单个静态库，不涉及库依赖，直接在gcc里面用-L参数引用即可；

/*
 * file: ffmpeglibtest.c
 *
 * author: openswc
 * http://blog.csdn.net/openswc
 *
 * gcc ffmpeglibtest.c -I./ffmpeg_build/include/ -L./ffmpeg_build/lib/ -lavutil -o ffmpeglibtest
 * gcc ffmpeglibtest.c -I /home/xxx/temp/ffmpeg-release-3.0/ffmpeg_build/include/ -L /home/xxx/temp/ffmpeg-release-3.0/ffmpeg_build/lib/ -lavutil -o ffmpeglibtest
*/
#include <stdio.h>

#include "libavutil/log.h"

int main()
{
	int iLogLev = 0;
 	iLogLev = av_log_get_level();
 	printf("av_log_get_level is *%d*\n", iLogLev);
 	av_log_set_level(AV_LOG_DEBUG);
	iLogLev = av_log_get_level();
	printf("av_log_set_level is *%d*\n", iLogLev);

 	return 0;
}

/*
 * file: ffmpeglibtestm.c
 *
 * author: openswc
 * http://blog.csdn.net/openswc
 *
 * gcc ffmpeglibtestm.c -I./ffmpeg_build/include/ -L./ffmpeg_build/lib/ -lavformat -lavcodec -lswresample -lavutil -pthread -lva -lm -lz -o ffmpeglibtestm
 * gcc ffmpeglibtestm.c -I /home/xxx/temp/ffmpeg-release-3.0/ffmpeg_build/include -L /home/xxx/temp/ffmpeg-release-3.0/ffmpeg_build/lib -lavformat -lavcodec -lswresample -lavutil -pthread -lva -lm -lz -o ffmpeglibtestm
*/

#include <stdio.h>

#include "libavutil/log.h"
#include "libavformat/avformat.h"


void test_log()
{

	av_register_all();

	AVFormatContext *obj=NULL;

	obj=avformat_alloc_context();

	printf("====================================\n");

	av_log(obj,AV_LOG_PANIC,"Panic: Something went really wrong and we will crash now.\n");

	av_log(obj,AV_LOG_FATAL,"Fatal: Something went wrong and recovery is not possible.\n");

	av_log(obj,AV_LOG_ERROR,"Error: Something went wrong and cannot losslessly be recovered.\n");

	av_log(obj,AV_LOG_WARNING,"Warning: This may or may not lead to problems.\n");

	av_log(obj,AV_LOG_INFO,"Info: Standard information.\n");

	av_log(obj,AV_LOG_VERBOSE,"Verbose: Detailed information.\n");

	av_log(obj,AV_LOG_DEBUG,"Debug: Stuff which is only useful for libav* developers.\n");

	printf("====================================\n");

	avformat_free_context(obj);

}

int main()
{
	int iLogLev = 0;

	iLogLev = av_log_get_level();
	printf("av_log_get_level is *%d*\n", iLogLev);
	av_log_set_level(AV_LOG_DEBUG);
	iLogLev = av_log_get_level();
	printf("av_log_set_level is *%d*\n", iLogLev);

	test_log();

	return 0;
}

如果引用多个ffmpeg库，则需要注意多个ffmepg库之间的依赖关系，那如何确定这个依赖关系呢？

找到该库的信息配置文件libxxx.pc，里面的Requires说明了需要依赖的库。

/ffmpeg-release-3.0/libavformat/http.c:626: undefined reference to `inflateEnd'
/ffmpeg-release-3.0/libavformat/http.c:627: undefined reference to `inflateInit2_'
/ffmpeg-release-3.0/libavformat/http.c:632: undefined reference to `zlibCompileFlags'

如果缺少-pthread，则会报以下undefined reference to错误；