深入了解android平台的jni---编译ffmpeg源码

环境：
操作系统：Ubuntu 10.04
ffmpeg源码版本：ffmpeg-0.6.1
android ndk版本：android-ndk-r5b-linux-x86
目的:
用来了解ffmpeg源码的编译场景和编译过程
准备工作:
将android-ndk-r5b解压后放在/home/mfcai目录下
在/home/mfcai/android-ndk-r5b/samples/目录下创建一个FFMPEG文件夹，在FFMPEG目录下再新建一个jni文件夹，然后把ffmpeg-0.6源码放在jni里面，所以最后ffmpeg源码的路径是:
/home/mfcai/android-ndk-r5b/samples/FFMPEG/jni/ffmpeg-0.6
一、设置NDK环境变量

配置NDK环境，增加/home/ndk目录到PATH环境变量：
$sudo gedit ~/.bashrc
文件底部添加以下两行：
NDK_ROOT=/home/mfcai/android-ndk-r5b
export NDK_ROOT
二、配置编译参数

在ffmpeg-0.6源文件夹下创建一个config.sh
config.sh是一个脚本，执行这个脚本的时候又调用了另外一个脚本configure，
configure主要是根据编译选项，生成相应的编译配置，即自己定制编译选项的内容。
1）新建一个config.sh
#!/bin/bash
PREBUILT=${NDK_ROOT}/toolchains/arm-eabi-4.4.0/prebuilt/linux-x86
PLATFORM=${NDK_ROOT}/platforms/android-8/arch-arm
./configure --target-os=linux \
--arch=arm \
--enable-version3 \
--enable-gpl \
--enable-nonfree \
--disable-stripping \
--disable-ffmpeg \
--disable-ffplay \
--disable-ffserver \
--disable-ffprobe \
--disable-encoders \
--disable-muxers \
--disable-devices \
--disable-protocols \
--enable-protocol=file \
--enable-avfilter \
--disable-network \
--disable-mpegaudio-hp \
--disable-avdevice \
--enable-cross-compile \
--cc=$PREBUILT/bin/arm-eabi-gcc \
--cross-prefix=$PREBUILT/bin/arm-eabi- \
--nm=$PREBUILT/bin/arm-eabi-nm \
--extra-cflags="-fPIC -DANDROID" \
--disable-asm \
--enable-neon \
--enable-armv5te \
--extra-ldflags="-Wl,-T,$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"
2)执行config.sh脚本文件
$ chmod +x config.sh
$ ./config.sh
如果配置正确的话显示出来的最后两行是这样的：
License: nonfree and unredistributable
Creating config.mak and config.h...
3)编辑config.h文件
编辑 /root/ffmpeg/jni/ffmpeg-0.6.1 目录中的 config.h 文件，
将#define restrict restrict修改为#define restrict
将
#define HAVE_LLRINT 0
#define HAVE_LLRINTF 0
#define HAVE_LRINT 0
#define HAVE_LRINTF 0
#define HAVE_ROUND 0
#define HAVE_ROUNDF 0
#define HAVE_TRUNCF 0
修改为：
#define HAVE_LLRINT 1
#define HAVE_LLRINTF 1
#define HAVE_LRINT 1
#define HAVE_LRINTF 1
#define HAVE_ROUND 1
#define HAVE_ROUNDF 1
#define HAVE_TRUNCF 1
三、准备编译ffmpeg1、编辑ffmpegffmpeg-0.6.1下各个模块的Makefile文件

分别把libavutil、libavcodec、libavformat、libavfilter、libpostproct和libswscale下的Makefile文件中下面两行删除掉：
include $(SUBDIR)../subdir.mak
include $(SUBDIR)../config.mak
2、在ffmpegffmpeg-0.6.1根目录下新建一个av.mk文件

# LOCAL_PATH is one of libavutil, libavcodec, libavformat, or libswscale
#include $(LOCAL_PATH)/../config-$(TARGET_ARCH).mak
include $(LOCAL_PATH)/../config.mak
OBJS :=
OBJS-yes :=
MMX-OBJS-yes :=
include $(LOCAL_PATH)/Makefile
# collect objects
OBJS-$(HAVE_MMX) += $(MMX-OBJS-yes)
OBJS += $(OBJS-yes)
FFNAME := lib$(NAME)
FFLIBS := $(foreach,NAME,$(FFLIBS),lib$(NAME))
FFCFLAGS = -DHAVE_AV_CONFIG_H -Wno-sign-compare -Wno-switch -Wno-pointer-sign
FFCFLAGS += -DTARGET_CONFIG=/"config-$(TARGET_ARCH).h/"
ALL_S_FILES := $(wildcard $(LOCAL_PATH)/$(TARGET_ARCH)/*.S)
ALL_S_FILES := $(addprefix $(TARGET_ARCH)/, $(notdir $(ALL_S_FILES)))
ifneq ($(ALL_S_FILES),)
ALL_S_OBJS := $(patsubst %.S,%.o,$(ALL_S_FILES))
C_OBJS := $(filter-out $(ALL_S_OBJS),$(OBJS))
S_OBJS := $(filter $(ALL_S_OBJS),$(OBJS))
else
C_OBJS := $(OBJS)
S_OBJS :=
endif
C_FILES := $(patsubst %.o,%.c,$(C_OBJS))
S_FILES := $(patsubst %.o,%.S,$(S_OBJS))
FFFILES := $(sort $(S_FILES)) $(sort $(C_FILES))
3、新建Android.mk文件

在jni目录建立Android.mk文件.
在ffmpegffmpeg-0.6.1下新建Android.mk文件
在libavformat,libavcodec,libavfilter、libavutil、libpostproc和libswscale目录建立同样的文件
1)在jni文件夹新建Android.mk文件
include $(all-subdir-makefiles)
2)在ffmpeg下新建Android.mk文件
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_WHOLE_STATIC_LIBRARIES := libavformat libavcodec libavutil libpostproc libswscale libavfilter
LOCAL_MODULE := ffmpeg
include $(BUILD_SHARED_LIBRARY)
include $(call all-makefiles-under,$(LOCAL_PATH))
3)在ffmpeg/libavformat下新建Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
include $(LOCAL_PATH)/../av.mk
LOCAL_SRC_FILES := $(FFFILES)
LOCAL_C_INCLUDES := \
$(LOCAL_PATH) \
$(LOCAL_PATH)/..
LOCAL_CFLAGS += $(FFCFLAGS)
LOCAL_CFLAGS += -include "string.h" -Dipv6mr_interface=ipv6mr_ifindex
LOCAL_LDLIBS := -lz
LOCAL_SHARED_LIBRARIES := libavutil libavcodec
LOCAL_MODULE := $(FFNAME)
include $(BUILD_SHARED_LIBRARY)
4)在ffmpeg/libavcodec下新建Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
include $(LOCAL_PATH)/../av.mk
LOCAL_SRC_FILES := $(FFFILES)
LOCAL_C_INCLUDES := \
$(LOCAL_PATH) \
$(LOCAL_PATH)/..
LOCAL_CFLAGS += $(FFCFLAGS)
LOCAL_LDLIBS := -lz
LOCAL_SHARED_LIBRARIES := libavutil
LOCAL_MODULE := $(FFNAME)
include $(BUILD_SHARED_LIBRARY)
5)在ffmpeg/libavfilter下新建Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
include $(LOCAL_PATH)/../av.mk
LOCAL_SRC_FILES := $(FFFILES)
LOCAL_C_INCLUDES := \
$(LOCAL_PATH) \
$(LOCAL_PATH)/..
LOCAL_CFLAGS += $(FFCFLAGS)
LOCAL_SHARED_LIBRARIES := libavutil libswscale libavcodec
LOCAL_MODULE := $(FFNAME)
include $(BUILD_SHARED_LIBRARY)
6)在ffmpeg/libavutil下新建Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
include $(LOCAL_PATH)/../av.mk
LOCAL_SRC_FILES := $(FFFILES)
LOCAL_C_INCLUDES := \
$(LOCAL_PATH) \
$(LOCAL_PATH)/..
LOCAL_CFLAGS += $(FFCFLAGS)
LOCAL_MODULE := $(FFNAME)
include $(BUILD_SHARED_LIBRARY)
7)在ffmpeg/libpostproc下新建Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
include $(LOCAL_PATH)/../av.mk
LOCAL_SRC_FILES := $(FFFILES)
LOCAL_C_INCLUDES := \
$(LOCAL_PATH) \
$(LOCAL_PATH)/..
LOCAL_CFLAGS += $(FFCFLAGS)
LOCAL_SHARED_LIBRARIES :=libavutil
LOCAL_MODULE := $(FFNAME)
include $(BUILD_SHARED_LIBRARY)
8)在ffmpeg/libswscale下的Android.mk文件
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
include $(LOCAL_PATH)/../av.mk
LOCAL_SRC_FILES := $(FFFILES)
LOCAL_C_INCLUDES := \
$(LOCAL_PATH) \
$(LOCAL_PATH)/..
LOCAL_CFLAGS += $(FFCFLAGS)
LOCAL_SHARED_LIBRARIES := libavutil
LOCAL_MODULE := $(FFNAME)
include $(BUILD_SHARED_LIBRARY)
四、编译

在jni目录下运行ndk-build
如果编译成功，产生出libavcodec.so、libavfilter.so、libavformat.so、libavutil.so、 libffmpeg.so，libpostproc.so和libswscale.so。

五、问题

1、同样的配置，在cygwin下编译了两天通不过。所以建议还是在linux环境下编译
2、libffmpeg.so大小只有1k。
网上的做法修改ffmpeg下的android.mk
发现出来的libffmpeg.so只有十几KB，按照网上搜索的资料，
方法一：修改ffmpeg下的android.mk：
LOCAL_STATIC_LIBRARIES := libavcodec libavformat libavutil libavfilter libpostproc libswscale
改后为：
LOCAL_WHOLE_STATIC_LIBRARIES := libavcodec libavformat libavutil libavfilter libpostproc libswscale
方法二：指定使用 arm-eabi-4.4.0 来编译：
由于android-ndk-r5 默认是使用 arm-linux-androideabi-4.4.3 编译，而不是 arm-eabi-4.4.0。
但 android-ndk-r5/toolchains/arm-linux-androideabi-4.4.3 目录中的 setup.mk 文件里定义的cmd-build-shared-library 函数
并没有将静态库文件链接在一起生成动态库文件。所以解决的办法就是在执行 ndk-build 时加上 NDK_TOOLCHAIN 参数，指定使用 arm-eabi-4.4.0 来编译。
完整命令如下
ndk-build NDK_TOOLCHAIN=arm-eabi-4.4.0 NDK_PLATFORM=android-8
同样不行。
希望高手能给指条道了
需要编译通过的ffmpeg-0.61文件的,请到
http://download.csdn.net/detail/mfcai_blog/5968953,下载 本文欢迎转载，转载请注明出处与作者
出处：http://blog.sina.com.cn/staratsky
作者：流星