用NDK编译FFmpeg

Android内置的编解码器实在太少，于是我们需要FFmpeg。Android提供了NDK，为我们使用FFmpeg这种C语言代码提供了方便。
首先创建一个标准的Android项目vPlayer

1. android create project -n vPlayer -t 8 -p vPlayer -k me.abitno.vplayer -a PlayerView

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然后在vPlayer目录里

1. mkdir jni && cd jni
   
2. wget http://ffmpeg.org/releases/ffmpeg-0.6.tar.bz2
   
3. tar xf ffmpeg-0.6.tar.bz2 && mv ffmpeg-0.6 ffmpeg && cd ffmpeg

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在ffmpeg下新建一个config.sh，内容如下，注意把PREBUILT和PLATFORM设置正确。另外里面有些参数你也可以自行调整，我主要是为了配置一个播放器而这样设置的。

1. #!/bin/bash
   
2. 
   
3. PREBUILT=/home/abitno/Android/android-ndk-r4/build/prebuilt/linux-x86/arm-eabi-4.4.0
   
4. PLATFORM=/home/abitno/Android/android-ndk-r4/build/platforms/android-8/arch-arm
   
5. 
   
6. ./configure --target-os=linux \
   
7.         --arch=arm \
   
8.         --enable-version3 \
   
9.         --enable-gpl \
   
10.         --enable-nonfree \
    
11.         --disable-stripping \
    
12.         --disable-ffmpeg \
    
13.         --disable-ffplay \
    
14.         --disable-ffserver \
    
15.         --disable-ffprobe \
    
16.         --disable-encoders \
    
17.         --disable-muxers \
    
18.         --disable-devices \
    
19.         --disable-protocols \
    
20.         --enable-protocol=file \
    
21.         --enable-avfilter \
    
22.         --disable-network \
    
23.         --disable-mpegaudio-hp \
    
24.         --disable-avdevice \
    
25.         --enable-cross-compile \
    
26.         --cc=$PREBUILT/bin/arm-eabi-gcc \
    
27.         --cross-prefix=$PREBUILT/bin/arm-eabi- \
    
28.         --nm=$PREBUILT/bin/arm-eabi-nm \
    
29.         --extra-cflags="-fPIC -DANDROID" \
    
30.         --disable-asm \
    
31.         --enable-neon \
    
32.         --enable-armv5te \
    
33.         --extra-ldflags="-Wl,-T,$PREBUILT/arm-eabi/lib/ldscripts/armelf.x -Wl,-rpath-link=$PLATFORM/usr/lib -L$PLATFORM/usr/lib -nostdlib $PREBUILT/lib/gcc/arm-eabi/4.4.0/crtbegin.o $PREBUILT/lib/gcc/arm-eabi/4.4.0/crtend.o -lc -lm -ldl"

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运行config.sh开始configure

1. chmod +x config.sh
   
2. ./config.sh

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configure完成后，编辑刚刚生成的config.h，找到这句

1. #define restrict restrict

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Android的GCC不支持restrict关键字，于是修改成下面这样

1. #define restrict

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编辑libavutil/libm.h，把其中的static方法都删除。

分别修改libavcodec、libavfilter、libavformat、libavutil、libpostproc和libswscale下的Makefile，把下面两句删除

1. include $(SUBDIR)../subdir.mak
   
2. include $(SUBDIR)../config.mak

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在ffmpeg下添加一个文件av.mk，内容如下

1. # LOCAL_PATH is one of libavutil, libavcodec, libavformat, or libswscale
   
2. 
   
3. #include $(LOCAL_PATH)/../config-$(TARGET_ARCH).mak
   
4. include $(LOCAL_PATH)/../config.mak
   
5. 
   
6. OBJS :=
   
7. OBJS-yes :=
   
8. MMX-OBJS-yes :=
   
9. include $(LOCAL_PATH)/Makefile
   
10. 
    
11. # collect objects
    
12. OBJS-$(HAVE_MMX) += $(MMX-OBJS-yes)
    
13. OBJS += $(OBJS-yes)
    
14. 
    
15. FFNAME := lib$(NAME)
    
16. FFLIBS := $(foreach,NAME,$(FFLIBS),lib$(NAME))
    
17. FFCFLAGS  = -DHAVE_AV_CONFIG_H -Wno-sign-compare -Wno-switch -Wno-pointer-sign
    
18. FFCFLAGS += -DTARGET_CONFIG=\"config-$(TARGET_ARCH).h\"
    
19. 
    
20. ALL_S_FILES := $(wildcard $(LOCAL_PATH)/$(TARGET_ARCH)/*.S)
    
21. ALL_S_FILES := $(addprefix $(TARGET_ARCH)/, $(notdir $(ALL_S_FILES)))
    
22. 
    
23. ifneq ($(ALL_S_FILES),)
    
24. ALL_S_OBJS := $(patsubst %.S,%.o,$(ALL_S_FILES))
    
25. C_OBJS := $(filter-out $(ALL_S_OBJS),$(OBJS))
    
26. S_OBJS := $(filter $(ALL_S_OBJS),$(OBJS))
    
27. else
    
28. C_OBJS := $(OBJS)
    
29. S_OBJS :=
    
30. endif
    
31. 
    
32. C_FILES := $(patsubst %.o,%.c,$(C_OBJS))
    
33. S_FILES := $(patsubst %.o,%.S,$(S_OBJS))
    
34. 
    
35. FFFILES := $(sort $(S_FILES)) $(sort $(C_FILES))

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接下来要添加一系列的Android.mk，在jni根目录下的内容如下

1. include $(all-subdir-makefiles)

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在ffmpeg目录下，Android.mk

1. LOCAL_PATH := $(call my-dir)
   
2. include $(CLEAR_VARS)
   
3. LOCAL_STATIC_LIBRARIES := libavformat libavcodec libavutil libpostproc libswscale
   
4. LOCAL_MODULE := ffmpeg
   
5. include $(BUILD_SHARED_LIBRARY)
   
6. include $(call all-makefiles-under,$(LOCAL_PATH))

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libavformat/Android.mk

1. LOCAL_PATH := $(call my-dir)
   
2. include $(CLEAR_VARS)
   
3. include $(LOCAL_PATH)/../av.mk
   
4. LOCAL_SRC_FILES := $(FFFILES)
   
5. LOCAL_C_INCLUDES :=                \
   
6.         $(LOCAL_PATH)                \
   
7.         $(LOCAL_PATH)/..
   
8. LOCAL_CFLAGS += $(FFCFLAGS)
   
9. LOCAL_CFLAGS += -include "string.h" -Dipv6mr_interface=ipv6mr_ifindex
   
10. LOCAL_LDLIBS := -lz
    
11. LOCAL_STATIC_LIBRARIES := $(FFLIBS)
    
12. LOCAL_MODULE := $(FFNAME)
    
13. include $(BUILD_STATIC_LIBRARY)

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libavcodec/Android.mk

1. LOCAL_PATH := $(call my-dir)
   
2. include $(CLEAR_VARS)
   
3. include $(LOCAL_PATH)/../av.mk
   
4. LOCAL_SRC_FILES := $(FFFILES)
   
5. LOCAL_C_INCLUDES :=                \
   
6.         $(LOCAL_PATH)                \
   
7.         $(LOCAL_PATH)/..
   
8. LOCAL_CFLAGS += $(FFCFLAGS)
   
9. LOCAL_LDLIBS := -lz
   
10. LOCAL_STATIC_LIBRARIES := $(FFLIBS)
    
11. LOCAL_MODULE := $(FFNAME)
    
12. include $(BUILD_STATIC_LIBRARY)

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libavfilter、libavutil、libpostproc和libswscale下的Android.mk内容如下

1. LOCAL_PATH := $(call my-dir)
   
2. include $(CLEAR_VARS)
   
3. include $(LOCAL_PATH)/../av.mk
   
4. LOCAL_SRC_FILES := $(FFFILES)
   
5. LOCAL_C_INCLUDES :=                \
   
6.         $(LOCAL_PATH)                \
   
7.         $(LOCAL_PATH)/..
   
8. LOCAL_CFLAGS += $(FFCFLAGS)
   
9. LOCAL_STATIC_LIBRARIES := $(FFLIBS)
   
10. LOCAL_MODULE := $(FFNAME)
    
11. include $(BUILD_STATIC_LIBRARY)

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最外层的jni/Android.mk和jni/ffmpeg/Android.mk只是随便这样写的，你应该根据自己的需求改写。