原文：http://blog.csdn.net/chinazjn/article/details/7954984
ffmpeg移植到dm365上，遇到undefined reference错误：
GA/gabin/lib/libavformat.a(allformats.o): In function `av_register_all':
/GA/ffmpeg-0.10/libavformat/allformats.c:53: undefined reference to `avcodec_register_all'
/GA/gabin/lib/libavformat.a(amr.o): In function `amr_read_packet':
/GA/ffmpeg-0.10/libavformat/amr.c:153: undefined reference to `av_new_packet'
/GA/ffmpeg-0.10/libavformat/amr.c:169: undefined reference to `av_free_packet'
/GA/gabin/lib/libavformat.a(anm.o): In function `read_header':
/GA/ffmpeg-0.10/libavformat/anm.c:89: undefined reference to `av_log_ask_for_sample'
/GA/ffmpeg-0.10/libavformat/anm.c:166: undefined reference to `av_log_ask_for_sample'
/GA/gabin/lib/libavformat.a(ape.o): In function `ape_read_packet':
/GA/ffmpeg-0.10/libavformat/ape.c:372: undefined reference to `av_new_packet'
/GA/gabin/lib/libavformat.a(applehttp.o): In function `free_variant_list':
/GA/ffmpeg-0.10/libavformat/applehttp.c:131: undefined reference to `av_free_packet'
/GA/gabin/lib/libavformat.a(applehttp.o): In function `reset_packet':
/GA/ffmpeg-0.10/libavformat/applehttp.c:151: undefined reference to `av_init_packet'
/GA/ffmpeg-0.10/libavformat/applehttp.c:151: undefined reference to `av_init_packet'
/GA/gabin/lib/libavformat.a(applehttp.o): In function `applehttp_read_seek':
/GA/ffmpeg-0.10/libavformat/applehttp.c:712: undefined reference to `av_free_packet'
/GA/gabin/lib/libavformat.a(applehttp.o): In function `reset_packet':
网上查阅，普遍提示两种解决方法：
一、ffmpeg是纯C的库，应用程序用C++来编译。
二、路径、需要的库包含不全。
以上具体就不说了，搜索下便是。
我在无数遍仔细确认上述两种可能性后，仍然报错。郁闷了一个晚上。。
后来查阅ffmpeg的 pkg-config，终于找到原因，错误导致过程让我痛苦，原因却很简单。
错误：gcc test.c -o test -I/GA/gabin/include/ -L/GA/gabin/lib -lavcodec -lavformat -lavdevice -lavutil -pthread -ldl -lswscale -lSDL -lbz2 -lasound -lz -lm
调整： gcc test.c -o test -I/GA/gabin/include/ -L/GA/gabin/lib -lavformat -lavdevice -lavcodec -lavutil -pthread -ldl -lswscale -lSDL -lbz2 -lasound -lz -lm
问题解决，同志需要注意包依赖关系。