用Android 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。

不过为了用NDK编译FFmpeg，还真的花费了不少时间，也得到了很多人的帮助，最应该谢谢havlenapetr
。我觉得我现在这些方法算是比较简洁的了－－

下面就尽量詳細的说一下我是怎么在项目中使用FFmpeg的，但是基于我混乱的表达能力，有不明白的就问我。

你得了解JNI和Android NDK的基本用法，若觉得我的文章还不错，可以看之前写的JNI简单入门
和Android NDK入门

首先创建一个标准的Android项目vPlayer

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

然后在vPlayer目录里

mkdir jni && cd jni

wget http://ffmpeg.org/releases/ffmpeg-0.6.tar.bz2 
tar xf ffmpeg-0.6.tar.bz2 && mv ffmpeg-0.6 ffmpeg && cd ffmpeg

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。

#!/bin/bash

PREBUILT=/home/abitno/Android/android-ndk-r4/build/prebuilt/linux-x86/arm-eabi-4.4.0

PLATFORM=/home/abitno/Android/android-ndk-r4/build/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"

运行config.sh开始configure

chmod +x config.sh

./config.sh

configure完成后，编辑刚刚生成的config.h，找到这句

#define restrict restrict

Android的GCC不支持restrict关键字，于是修改成下面这样

#define restrict

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

include $(SUBDIR)../subdir.mak

include $(SUBDIR)../config.mak

在ffmpeg下添加一个文件av.mk，内容如下

# 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))

接下来要添加一系列的Android.mk，在jni根目录下的内容如下

include $(all-subdir-makefiles)

在ffmpeg目录下，Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_STATIC_LIBRARIES := libavformat libavcodec libavutil libpostproc libswscale

LOCAL_MODULE := ffmpeg

include $(BUILD_SHARED_LIBRARY)

include $(call all-makefiles-under,$(LOCAL_PATH))

libavformat/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_STATIC_LIBRARIES := $(FFLIBS)

LOCAL_MODULE := $(FFNAME)

include $(BUILD_STATIC_LIBRARY)

libavcodec/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_STATIC_LIBRARIES := $(FFLIBS)

LOCAL_MODULE := $(FFNAME)

include $(BUILD_STATIC_LIBRARY)

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

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_STATIC_LIBRARIES := $(FFLIBS)

LOCAL_MODULE := $(FFNAME)

include $(BUILD_STATIC_LIBRARY)

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

最后运行ndk-build，经过漫长的等待就编译完成了。至于具体怎么应用可能以后会写，我变得太懒了。。。

我已经尽最大努力写明白了，希望大家努力啊，一个全功能的解码器或者只是播放器还是很有必要的。