准备环节：

1. 编译环境为Linux，笔者用的是Ubuntu16.04；
2. 确保NDK环境配置可用；
3. 下载好FFmpeg 和x264的源码；

需要的环境和文件准备好了之后，就可以开始准备编译咯
为了让编译得到的库能适合Android，需要修改配置文件ffmpeg/configure

#SLIBNAME_WITH_MAJOR='$(SLIBNAME).$(LIBMAJOR)'
SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'

#LIB_INSTALL_EXTRA_CMD='$$(RANLIB) "$(LIBDIR)/$(LIBNAME)"'
LIB_INSTALL_EXTRA_CMD='$$(RANLIB)"$(LIBDIR)/$(LIBNAME)"'

#SLIB_INSTALL_NAME='$(SLIBNAME_WITH_VERSION)'
SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'

#SLIB_INSTALL_LINKS='$(SLIBNAME_WITH_MAJOR) $(SLIBNAME)'
SLIB_INSTALL_LINKS='$(SLIBNAME)'

• 在jni目录下面创建一个文件build_ffmpeg_with_x264.sh，用于配置环境变量和控制编译主流程；
• 在x264目录下面创建一个文件build_x264_for_android.sh，用于编译x264；
• 在ffmpeg目录下面创建一个文件build_ffmpeg_for_android.sh，用于编译ffmpeg；

这样就可以编译出ffmpeg的库，如果在编译时提醒需要什么工具，直接安装完之后再重新执行脚本。

上面说到三个文件现在来逐一解析一下。

首先，看看build_ffmpeg_with_x264.sh，从文件名可以看出，该脚本就是把ffmpeg和x264混合编译。

#!/bin/bash

#配置NDK路径
export NDK=/opt/Sdk/ndk-bundle

# 检测NDK
if [[  -z "$NDK"  ]]; then
    echo "The NDK dir is empty, If the shell can not run normally, you should set the NDK variable to your local ndk.dir"
    exit 1
fi

# 检测系统
OS=`uname`
HOST_ARCH=`uname -m`
export CCACHE=; type ccache >/dev/null 2>&1 && export CCACHE=ccache
if [ $OS == 'Linux' ]; then
    export HOST_SYSTEM=linux-$HOST_ARCH
elif [ $OS == 'Darwin' ]; then
    export HOST_SYSTEM=darwin-$HOST_ARCH
fi

# 配置 SYSROOT 和 CROSS_PREFIX，基于android-15
SYSROOT=$NDK/platforms/android-15/arch-arm
CROSS_PREFIX=$NDK/toolchains/arm-linux-androideabi-4.9/prebuilt/$HOST_SYSTEM/bin/arm-linux-androideabi-
echo "CROSS_PREFIX=$CROSS_PREFIX"


ROOT_DIR=`pwd`/
COMMOND_DIR=command_source
echo $ROOT_DIR

#配置输出路径
PREFIX=$ROOT_DIR/build
if [[ ! -d "$PREFIX" ]]; then
    mkdir $PREFIX
fi

#### 编译步骤 开始 ####
#1、编译x264
#2、编译ffmpeg
#3、ndk-build
#### 编译步骤 结束 ####


#预先编译x264，编译类型为静态库#
X264_SOURCE_DIR=x264
if [[ ! -d "$X264_SOURCE_DIR" ]]; then
    git clone http://git.videolan.org/git/x264.git $X264_SOURCE_DIR
fi
cp $ROOT_DIR$COMMOND_DIR/build_x264_for_android.sh $X264_SOURCE_DIR/build_x264_for_android.sh
TARGET_X264_DIR=$ROOT_DIR$X264_SOURCE_DIR
source $X264_SOURCE_DIR/build_x264_for_android.sh


#编译ffmpeg，编译为多个静态库#
FFMPEG_SOURCE_DIR=ffmpeg-3.3
if [[ ! -d "$FFMPEG_SOURCE_DIR" ]]; then
    git clone git://source.ffmpeg.org/ffmpeg.git $FFMPEG_SOURCE_DIR
fi
cp $ROOT_DIR$COMMOND_DIR/build_for_android.sh $FFMPEG_SOURCE_DIR/build_for_android.sh
TARGET_FFMPEG_DIR=$ROOT_DIR$FFMPEG_SOURCE_DIR
source $FFMPEG_SOURCE_DIR/build_ffmpeg_for_android.sh

#执行ndk-build
$NDK/ndk-build

build_x264_for_android.sh文件内容如下：

#!/bin/bash

echo "###### 开始编译 x264 ######"

SOURCE=$TARGET_X264_DIR
echo $SOURCE
cd $SOURCE

EXTRA_CFLAGS="-march=armv7-a -mfloat-abi=softfp -mfpu=neon -D__ARM_ARCH_7__ -D__ARM_ARCH_7A__"
EXTRA_LDFLAGS="-nostdlib"

./configure \
配置输出路径
    --prefix=$PREFIX \
配置交叉编译路径前缀
    --cross-prefix=$CROSS_PREFIX \
    --extra-cflags="$EXTRA_CFLAGS" \
    --extra-ldflags="$EXTRA_LDFLAGS" \
    --enable-static \
    --enable-pic \
    --enable-strip \
    --disable-cli \
    --host=arm-linux \
    --sysroot=$SYSROOT

make clean
make && make install

echo "###### x264编译完成 ######"
cd ../

运行前需要把上面的两行中文注释删除，因为configure中间不能有注释，所以我就直接没有加#来注释，便于发现问题。

build_ffmpeg_for_android.sh文件内容如下：

#!/bin/bash

echo "###### 开始编译 ffmpeg ######"

SOURCE=$TARGET_FFMPEG_DIR
echo $SOURCE
cd $SOURCE


ADD_H264_FEATURE="--enable-encoder=aac \
    --enable-decoder=aac \
    --enable-gpl \
    --enable-encoder=libx264 \
    --enable-libx264 \
    --extra-cflags=-I$PREFIX/include \
    --extra-ldflags=-L$PREFIX/lib "

function build_one_so
{
    ./configure \
        --prefix=$PREFIX \
        --disable-shared \
        --enable-pthreads \
        --enable-gpl \
        --enable-version3 \
        --enable-nonfree \
        --enable-static \
        --enable-ffmpeg \
        --disable-ffplay \
        --disable-ffprobe \
        --disable-ffserver \
        --disable-doc \
        --disable-symver \
        --enable-avdevice \
        --enable-avfilter \
        --enable-libx264 \
        --enable-small \
        --enable-asm \
        --enable-neon \
        --cross-prefix=$CROSS_PREFIX \
        --target-os=linux \
        --arch=arm \
        --enable-cross-compile \
        --enable-runtime-cpudetect \
        --sysroot=$SYSROOT \
        --disable-parsers \
        --enable-parser=aac \
        --enable-parser=h264 \
        --enable-parser=mjpeg \
        --enable-parser=png \
        --enable-parser=bmp \
        --enable-parser=mpegvideo \
        --enable-parser=mpegaudio \
        --disable-encoders \
        --enable-encoder=h263 \
        --enable-encoder=libx264 \
        --enable-encoder=mpeg4 \
        --enable-encoder=aac \
        --enable-encoder=png \
        --enable-encoder=gif \
        --enable-encoder=bmp \
        --disable-decoders \
        --enable-decoder=h263 \
        --enable-decoder=h264 \
        --enable-decoder=mpeg4 \
        --enable-decoder=mjpeg \
        --enable-decoder=gif \
        --enable-decoder=mp3 \
        --enable-decoder=aac \
        --enable-decoder=png \
        --enable-decoder=bmp \
        --enable-decoder=yuv4 \
        --disable-network \
        --enable-protocols \
        --enable-protocol=concat \
        --enable-protocol=hls \
        --enable-protocol=file \
        --disable-demuxers \
        --enable-demuxer=h263 \
        --enable-demuxer=h264 \
        --enable-demuxer=flv \
        --enable-demuxer=gif \
        --enable-demuxer=aac \
        --enable-demuxer=ogg \
        --enable-demuxer=dts \
        --enable-demuxer=mp3 \
        --enable-demuxer=mov \
        --enable-demuxer=m4v \
        --enable-demuxer=concat \
        --enable-demuxer=mpegts \
        --enable-demuxer=mjpeg \
        --enable-demuxer=mpegvideo \
        --enable-demuxer=rawvideo \
        --enable-demuxer=yuv4mpegpipe \
        --disable-muxers \
        --enable-muxer=h264 \
        --enable-muxer=flv \
        --enable-muxer=gif \
        --enable-muxer=mp3 \
        --enable-muxer=dts \
        --enable-muxer=mp4 \
        --enable-muxer=mov \
        --enable-muxer=mpegts \
        --disable-filters \
        --enable-filter=aresample \
        --enable-filter=asetpts \
        --enable-filter=setpts \
        --enable-filter=ass \
        --enable-filter=scale \
        --enable-filter=concat \
        --enable-filter=atempo \
        --enable-filter=movie \
        --enable-filter=overlay \
        --enable-filter=rotate \
        --enable-filter=transpose \
        --enable-filter=hflip \
        --extra-cflags="-mfloat-abi=softfp -mfpu=neon -marm -march=armv7-a" \
        $ADD_H264_FEATURE

    make clean
    make -j4
    make install
}

build_one_so

echo "###### ffmpeg编译完成 ######"
cd ../

这个脚本稍微多一点，主要是对ffmpeg的定制，由于ffmpeg全部功能打开的话，最终生成的库会很大，通常我们需要根据需求，对ffmpeg进行定制裁剪，根据encoder，decoder，muxer，demuxer，parser，filter，protocol等七个方面进行。首先都会全部disable，然后根据需求再enable需要的格式和功能。

上面是编译ffmpeg需要的配置，为了编译出Android可用的so文件，还需要配置Android.mk文件

LOCAL_PATH := $(call my-dir)

#include $(call all-subdir-makefiles)

#static version of libavcodec
include $(CLEAR_VARS)
LOCAL_MODULE:= libavcodec_static
LOCAL_SRC_FILES:= ./build/lib/libavcodec.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)

#static version of libavformat
include $(CLEAR_VARS)
LOCAL_MODULE:= libavformat_static
LOCAL_SRC_FILES:= ./build/lib/libavformat.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)

#static version of libswscale
include $(CLEAR_VARS)
LOCAL_MODULE:= libswscale_static
LOCAL_SRC_FILES:= ./build/lib/libswscale.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)

#static version of libavutil
include $(CLEAR_VARS)
LOCAL_MODULE:= libavutil_static
LOCAL_SRC_FILES:= ./build/lib/libavutil.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)

#static version of libavdevice
include $(CLEAR_VARS)
LOCAL_MODULE:= libavdevice_static
LOCAL_SRC_FILES:= ./build/lib/libavdevice.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)

#static version of libavfilter
include $(CLEAR_VARS)
LOCAL_MODULE:= libavfilter_static
LOCAL_SRC_FILES:= ./build/lib/libavfilter.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)

#static version of libswresample
include $(CLEAR_VARS)
LOCAL_MODULE:= libswresample_static
LOCAL_SRC_FILES:= ./build/lib/libswresample.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)

#static version of libpostproc
include $(CLEAR_VARS)
LOCAL_MODULE:= libpostproc_static
LOCAL_SRC_FILES:= ./build/lib/libpostproc.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)

#static version of libx264
include $(CLEAR_VARS)
LOCAL_MODULE:= libx264_static
LOCAL_SRC_FILES:= ./build/lib/libx264.a
LOCAL_CFLAGS := -march=armv7-a -mfloat-abi=softfp -mfpu=neon -O3 -ffast-math -funroll-loops
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
include $(PREBUILT_STATIC_LIBRARY)


include $(CLEAR_VARS)
LOCAL_MODULE := ffmpeg
LOCAL_C_INCLUDES := ./build/include \
LOCAL_SRC_FILES := decoder.c encoder.c
LOCAL_LDLIBS := -llog -lz
LOCAL_CFLAGS := -march=armv7-a -mfloat-abi=softfp -mfpu=neon -O3 -ffast-math -funroll-loops
LOCAL_WHOLE_STATIC_LIBRARIES := libavformat_static \
                        libavcodec_static \
                        libavutil_static \
                        libpostproc_static \
                        libswscale_static \
                        libswresample_static \
                        libx264_static \
                        libavfilter_static \
                        libavdevice_static \
                        
include $(BUILD_SHARED_LIBRARY)

还需要一个Application.mk文件

APP_ABI := armeabi-v7a
APP_PLATFORM := android-15
# system - 使用默认最小的C++运行库，这样生成的应用体积小，内存占用小，但部分功能将无法支持
# stlport_static - 使用STLport作为静态库，这项是Android开发网极力推荐的
# stlport_shared - STLport 作为动态库，这个可能产生兼容性和部分低版本的Android固件，目前不推荐使用。
# gnustl_static - 使用 GNU libstdc++ 作为静态库
# 使用STLport作为静态库，这项是Android开发网极力推荐的
#APP_STL := stlport_static
APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -std=gnu++11
APP_OPTIM := release

这样配置完成后的目录结构如下：

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