When compiling libfaac with GCC you get: g++ -DHAVE_CONFIG_H -I. -I../.. -I../../include -Wall -g -O2 -MT 3gp.o -MD -MP -MF .deps/3gp.Tpo -c -o 3gp.o 3gp.cpp In file included from mp4common.h:29:0, from 3gp.cpp:28: mpeg4ip.h:126:58: error: new declaration ‘char* strcasestr(const char*, const char*)’ /usr/include/string.h:369:28: error: ambiguates old declaration ‘const char* strcasestr(const char*, const char*)’ make[3]: *** [3gp.o] Error 1 Solution is to remove the declaration of strcasestr() in commom/mp4v2/mpeg4ip.h (suggested here).