ubuntu编译遇到的问题

一.ffmpeg链接不到库文件

undefined reference to `avcodec_register_all'
undefined reference to `avcodec_register_all'
undefined reference to `av_opt_set_defaults'
undefined reference to `av_opt_set_defaults'
undefined reference to `av_parse_video_frame_rate'
undefined reference to `av_parse_video_frame_size'
undefined reference to `avcodec_string'
undefined reference to `avcodec_alloc_context'
undefined reference to `av_fast_realloc'
undefined reference to `av_get_bits_per_sample'
undefined reference to `av_parser_close'
undefined reference to `av_parser_close'

问题分析：函数实现在.c文件中，需要将相关的头文件使用extern "C" { }包含起来。

extern "C"
{
#include <libavutil/frame.h>
#include <libavutil/mem.h>
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
}