【问题标题】：FFMPEG Link errorFFMPEG 链接错误
【发布时间】：2014-11-02 18:10:00
【问题描述】：

我正在尝试编译这个transcoding example from the FFMPEG site 的修改版本，我已经使用了所有必需的包含并使用它加入了库：

INCLUDEPATH += $$(FFMPEG_DEV_PATH)\include
    LIBS += -L$$(FFMPEG_DEV_PATH)\lib -lavformat -lavcodec -lavutil -lswscale -liconv -lz -lavfilter

但我收到了这个我无法理解的链接错误：

  "avio_close(AVIOContext*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "av_strerror(int, char*, unsigned long)", referenced from:
      av_make_error_string(char*, unsigned long, int) in PhVideoEncoder.o
  "av_rescale_q(long long, AVRational, AVRational)", referenced from:
      PhVideoEncoder::encode_write_frame(AVFrame*, unsigned int, int*) in PhVideoEncoder.o
  "av_frame_free(AVFrame**)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
      PhVideoEncoder::filter_encode_write_frame(AVFrame*, unsigned int) in PhVideoEncoder.o
      PhVideoEncoder::encode_write_frame(AVFrame*, unsigned int, int*) in PhVideoEncoder.o
  "av_read_frame(AVFormatContext*, AVPacket*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "avcodec_close(AVCodecContext*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "avcodec_open2(AVCodecContext*, AVCodec const*, AVDictionary**)", referenced from:
      PhVideoEncoder::open_input_file(char const*) in PhVideoEncoder.o
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o
  "av_dump_format(AVFormatContext*, int, char const*, int)", referenced from:
      PhVideoEncoder::open_input_file(char const*) in PhVideoEncoder.o
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o
  "av_frame_alloc()", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
      PhVideoEncoder::filter_encode_write_frame(AVFrame*, unsigned int) in PhVideoEncoder.o
  "av_free_packet(AVPacket*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "av_init_packet(AVPacket*)", referenced from:
      PhVideoEncoder::encode_write_frame(AVFrame*, unsigned int, int*) in PhVideoEncoder.o
  "av_opt_set_bin(void*, char const*, unsigned char const*, int, int)", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "av_register_all()", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "av_rescale_q_rnd(long long, AVRational, AVRational, AVRounding)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
      PhVideoEncoder::encode_write_frame(AVFrame*, unsigned int, int*) in PhVideoEncoder.o
  "av_write_trailer(AVFormatContext*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "avfilter_graph_free(AVFilterGraph**)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "avfilter_inout_free(AVFilterInOut**)", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "avformat_new_stream(AVFormatContext*, AVCodec const*)", referenced from:
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o
  "avformat_open_input(AVFormatContext**, char const*, AVInputFormat*, AVDictionary**)", referenced from:
      PhVideoEncoder::open_input_file(char const*) in PhVideoEncoder.o
  "avcodec_copy_context(AVCodecContext*, AVCodecContext const*)", referenced from:
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o
  "avcodec_find_decoder(AVCodecID)", referenced from:
      PhVideoEncoder::open_input_file(char const*) in PhVideoEncoder.o
  "avcodec_find_encoder(AVCodecID)", referenced from:
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o
  "avfilter_get_by_name(char const*)", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "avfilter_graph_alloc()", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "avfilter_inout_alloc()", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "avformat_close_input(AVFormatContext**)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "avcodec_decode_audio4(AVCodecContext*, AVFrame*, int*, AVPacket const*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "avcodec_decode_video2(AVCodecContext*, AVFrame*, int*, AVPacket const*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "avcodec_encode_audio2(AVCodecContext*, AVPacket*, AVFrame const*, int*)", referenced from:
      PhVideoEncoder::encode_write_frame(AVFrame*, unsigned int, int*) in PhVideoEncoder.o
  "avcodec_encode_video2(AVCodecContext*, AVPacket*, AVFrame const*, int*)", referenced from:
      PhVideoEncoder::encode_write_frame(AVFrame*, unsigned int, int*) in PhVideoEncoder.o
  "avfilter_graph_config(AVFilterGraph*, void*)", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "avfilter_register_all()", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "avformat_free_context(AVFormatContext*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "avformat_write_header(AVFormatContext*, AVDictionary**)", referenced from:
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o
  "av_get_sample_fmt_name(AVSampleFormat)", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "av_buffersink_get_frame(AVFilterContext*, AVFrame*)", referenced from:
      PhVideoEncoder::filter_encode_write_frame(AVFrame*, unsigned int) in PhVideoEncoder.o
  "avfilter_graph_parse_ptr(AVFilterGraph*, char const*, AVFilterInOut**, AVFilterInOut**, void*)", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "avformat_find_stream_info(AVFormatContext*, AVDictionary**)", referenced from:
      PhVideoEncoder::open_input_file(char const*) in PhVideoEncoder.o
  "av_interleaved_write_frame(AVFormatContext*, AVPacket*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
      PhVideoEncoder::encode_write_frame(AVFrame*, unsigned int, int*) in PhVideoEncoder.o
  "av_buffersrc_add_frame_flags(AVFilterContext*, AVFrame*, int)", referenced from:
      PhVideoEncoder::filter_encode_write_frame(AVFrame*, unsigned int) in PhVideoEncoder.o
  "avfilter_graph_create_filter(AVFilterContext**, AVFilter const*, char const*, char const*, void*, AVFilterGraph*)", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "av_get_default_channel_layout(int)", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "avformat_alloc_output_context2(AVFormatContext**, AVOutputFormat*, char const*, char const*)", referenced from:
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o
  "av_get_channel_layout_nb_channels(unsigned long long)", referenced from:
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o
  "av_frame_get_best_effort_timestamp(AVFrame const*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "av_log(void*, int, char const*, ...)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
      PhVideoEncoder::filter_encode_write_frame(AVFrame*, unsigned int) in PhVideoEncoder.o
      PhVideoEncoder::flush_encoder(unsigned int) in PhVideoEncoder.o
      PhVideoEncoder::open_input_file(char const*) in PhVideoEncoder.o
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
      PhVideoEncoder::encode_write_frame(AVFrame*, unsigned int, int*) in PhVideoEncoder.o
      ...
  "av_free(void*)", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "av_malloc(unsigned long)", referenced from:
      av_malloc_array(unsigned long, unsigned long) in PhVideoEncoder.o
  "av_strdup(char const*)", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "avio_open(AVIOContext**, char const*, int)", referenced from:
      PhVideoEncoder::open_output_file(char const*) in PhVideoEncoder.o

我尝试寻找丢失的库，但没有运气......我错过了什么？

编辑

感谢第一个答案，我添加了 extern C 的东西，但我仍然面临一些错误：

Undefined symbols for architecture x86_64:
  "_av_buffersink_get_frame", referenced from:
      PhVideoEncoder::filter_encode_write_frame(AVFrame*, unsigned int) in PhVideoEncoder.o
  "_av_buffersrc_add_frame_flags", referenced from:
      PhVideoEncoder::filter_encode_write_frame(AVFrame*, unsigned int) in PhVideoEncoder.o
  "_avfilter_get_by_name", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "_avfilter_graph_alloc", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "_avfilter_graph_config", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "_avfilter_graph_create_filter", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "_avfilter_graph_free", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
  "_avfilter_graph_parse_ptr", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "_avfilter_inout_alloc", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "_avfilter_inout_free", referenced from:
      PhVideoEncoder::init_filter(FilteringContext*, AVCodecContext*, AVCodecContext*, char const*) in PhVideoEncoder.o
  "_avfilter_register_all", referenced from:
      PhVideoEncoder::PhVideoEncoder(QString) in PhVideoEncoder.o
ld: symbol(s) not found for architecture x86_64

【问题讨论】：

标签： linker ffmpeg libraries

【解决方案1】：

带有转码示例的 FFmpeg 站点的链接现已损坏，但您可以在此处找到它：http://ffmpeg.org/doxygen/trunk/doc_2examples_2transcoding_8c-example.html

我认为问题在于该示例使用了更高版本的 FFmpeg。我正在使用来自https://github.com/appunite/AndroidFFmpeg 的FFmpeg 1.0 的Android 端口，我也面临同样的问题（即未声明的avfilter_graph_parse_ptr）。我的 FFmpeg 源代码没有它，而是声明了avfilter_graph_parse。

我的源代码没有转码示例，我认为应该使用 doc/examples/decoding_encoding.c。

我更改了代码以使用旧函数，例如 example av_frame_free -> avcodec_free_frame、av_buffersrc_write_frame_flags -> av_buffersrc_write_frame 等等，现在它至少可以编译...

【讨论】：

【解决方案2】：

请参阅this post - 很可能在将 C++ 代码与 FFMPEG 的 C 接口混合时，您忘记了 extern "C" 关键字，因此链接器正在使用 C++ 函数名称修改，因此无法找到引用。您应该像这样用extern "C" 包装 FFMPEG 包含：

extern "C" { 
#include <libavcodec/avcodec.h> 
#include <libavformat/avformat.h>
}

【讨论】：

先生，您应该获得奖章。但是我面临更多错误，您的惊人答案没有解决这些错误。我将编辑我的问题
@Thomas 您链接的是 32 位 FFMPEG 还是 64 位？看来您的应用和 FFMPEG 具有不同的架构。
我不知道应该在哪里找到它？
如果我假设您使用的是 Mac OS/Linux 是正确的，您可以使用 otool 转储 FFMPEG .so 文件以确定版本 - 参见 stackoverflow.com/questions/12001195/… 。您使用的是什么操作系统（我对 Mac OS X 的假设是否正确）？您从哪里获得 FFMPEG 库（在 Linux 上，打包系统应该安装正确的架构，在 Mac OS X 上我实际上不知道您如何获得 FFMPEG 的二进制文件）？如果您从源代码构建它，您是否正确构建它？
是的，我正在运行 Mac OS 10.9.4。我使用 brew 安装（下载和编译）软件包，它与我的其他软件配合得很好。