未定义引用错误，无法创建共享库

Question

尝试了很多方法来解决问题，但没有运气。这是我的 Android.mk：

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)  
LOCAL_MODULE := avcodec
LOCAL_SRC_FILES :=libavcodec.a
include $(PREBUILT_STATIC_LIBRARY)

include $(CLEAR_VARS)   
LOCAL_MODULE := avutil
LOCAL_SRC_FILES :=libavutil.a
include $(PREBUILT_STATIC_LIBRARY)

include $(CLEAR_VARS) 
LOCAL_MODULE := swscale
LOCAL_SRC_FILES :=libswscale.a
include $(PREBUILT_STATIC_LIBRARY)

include $(CLEAR_VARS)  
LOCAL_MODULE := avformat
LOCAL_SRC_FILES :=libavformat.a
include $(PREBUILT_STATIC_LIBRARY)

include $(CLEAR_VARS)   
LOCAL_MODULE := avresample
LOCAL_SRC_FILES :=libavresample.a
include $(PREBUILT_STATIC_LIBRARY)


include $(CLEAR_VARS)   
LOCAL_MODULE := swresample
LOCAL_SRC_FILES :=libswresample.a
include $(PREBUILT_STATIC_LIBRARY)

include $(CLEAR_VARS) 
LOCAL_MODULE :=     x264
LOCAL_SRC_FILES :=libx264.a
include $(PREBUILT_STATIC_LIBRARY)

include $(CLEAR_VARS)  
#------------------------------------------
LOCAL_C_INCLUDES := $(LOCAL_PATH)\
$(LOCAL_PATH)/include

LOCAL_MODULE    := media

LOCAL_SRC_FILES := \
P_Decoding.cpp \
P_Encoding.cpp \
wrapper_for_ffmpeg.cpp

LOCAL_CPPFLAGS := -std=c++11 -pthread -frtti -fexceptions

LOCAL_ARM_MODE := arm 

LOCAL_STATIC_LIBRARIES := avcodec avutil swscale avformat avresample swresample x264

LOCAL_LDLIBS :=  -llog -ljnigraphics -landroid -lz -lEGL

LOCAL_CPP_FEATURES :=  rtti exceptions 

include $(BUILD_SHARED_LIBRARY)

在 jni 文件夹中，有所有与 makefile 上的 .cpp 文件相关的头 .hpp 文件，还有所有静态 .a 库和所有与静态库相关的头文件的“include”文件夹。我正在使用 ndk9c 版本。 这是错误日志的一部分：

[armeabi-v7a] Compile++ thumb: media <= P_Decoding.cpp
[armeabi-v7a] Compile++ thumb: media <= P_Encoding.cpp
[armeabi-v7a] Compile++ thumb: media <= wrapper_for_ffmpeg.cpp

/home/pro/android-ndk-r9c/toolchains/llvm-3.3/prebuilt/linux-x86/bin/clang++ -Wl,-soname,libmedia.so -shared --sysroot=/home/pro/android -ndk-r9c/platforms/android-9/arch-arm ./obj/local/armeabi/objs/media/P_Decoding.o ./obj/local/armeabi/objs/media/P_Encoding.o jni/libavformat.a jni /libavcodec.a jni/libavutil.a jni/libswscale.a -lgcc ./obj/local/armeabi/libgnustl_shared.so -gcc-toolchain /home/pro/android-ndk-r9c/toolchains/arm-linux-androideabi- 4.8/prebuilt/linux-x86 -no-canonical-prefixes -target armv5te-none-linux-androideabi -Wl,--no-undefined -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,现在 -L/home/pro/android-ndk-r9c/platforms/android-9/arch-arm/usr/lib -llog -ljnigraphics -lz -ldl -lgcc /home/pro/android-ndk-r9c/sources/ cxx-stl/gnu-libstdc++/4.8/libs/armeabi/libsupc++.a -lc -lm -o ./obj/local/armeabi/libmedia.so

jni/P_Decoding.cpp:10: error: undefined reference to 'avcodec_register_all'
jni/P_Decoding.cpp:17: error: undefined reference to 'avcodec_find_decoder'
jni/P_Decoding.cpp:14: error: undefined reference to 'avcodec_find_decoder_by_name'
jni/P_Decoding.cpp:24: error: undefined reference to 'avcodec_alloc_context3'
jni/P_Decoding.cpp:50: error: undefined reference to 'avcodec_open2'
jni/P_Decoding.cpp:56: error: undefined reference to 'avcodec_alloc_frame'
jni/P_Decoding.cpp:76: error: undefined reference to 'sws_getContext'
jni/P_Decoding.cpp:90: error: undefined reference to 'avcodec_decode_video2'
jni/P_Decoding.cpp:104: error: undefined reference to 'sws_scale'
jni/P_Decoding.cpp:118: error: undefined reference to 'avcodec_close'

请帮忙。提前致谢

Answer 1

确保您在 libavcodec 和 swscale 标头的包含周围添加了 extern "C" 块，例如像这样：

extern "C" {
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>
}

请参阅 https://libav.org/faq.html#I_0027m-using-Libav-from-within-my-C_002b_002b-application-but-the-linker-complains-about-missing-symbols-which-seem-to-be-available_002e 了解相关说明。

---

编辑：另外，您确定预构建的 libavcodec.a 与您正在构建的架构 (armeabi-v7a) 相同吗？如果您要为多种架构（armeabi-v7a、x86 等）构建共享库，您还需要有多个对应版本的预构建库。

Answer 2

尝试ndk-build V=1 查看链接库的实际命令。你想以

结束

-lavformat -lavcodec -lavfilter -lavutil -lswscale

按此顺序（如 here），但我不确定 avresample swresample x264 应该放在哪里。相应地重新排列您的 LOCAL_STATIC_LIBRARIES。