macOS上为Android编译ffmpeg so库

1.下载
http://www.ffmpeg.org/download.html
tar -xzf [解压下载的文件]

2.配置并编写编译指令
（1）安装 yasm
brew install yasm
（2）编辑configure文件
将该文件中的如下四行：

SLIBNAME_WITH_MAJOR='$(SLIBNAME).$(LIBMAJOR)'
LIB_INSTALL_EXTRA_CMD='$$(RANLIB)"$(LIBDIR)/$(LIBNAME)"'
SLIB_INSTALL_NAME='$(SLIBNAME_WITH_VERSION)'
SLIB_INSTALL_LINKS='$(SLIBNAME_WITH_MAJOR)$(SLIBNAME)'

替换为：

SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'
LIB_INSTALL_EXTRA_CMD='$$(RANLIB) "$(LIBDIR)/$(LIBNAME)"'
SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'
SLIB_INSTALL_LINKS='$(SLIBNAME)'

安装完毕后执行./configure
(3)新建android_build.sh文件，编辑android_build.sh

#!/bin/bash
make clean
export NDK=/Users/xusu/Library/Android/sdk/ndk/21.1.6352462
export SYSROOT=$NDK/platforms/android-29/arch-arm/
export TOOLCHAIN=$NDK/toolchains/arm-linux-androideabi-4.9/prebuilt/darwin-x86_64
export CPU=arm
export PREFIX=$(pwd)/android/$CPU
export ADDI_CFLAGS="-marm"
./configure --target-os=linux \
--prefix=$PREFIX --arch=arm \
--disable-doc \
--enable-shared \
--disable-static \
--disable-yasm \
--disable-symver \
--enable-gpl \
--disable-ffmpeg \
--disable-ffplay \
--disable-ffprobe \
--disable-ffserver \
--disable-doc \
--disable-symver \
--cross-prefix=$TOOLCHAIN/bin/arm-linux-androideabi- \
--enable-cross-compile \
--sysroot=$SYSROOT \
--extra-cflags="-Os -fpic $ADDI_CFLAGS" \
--extra-ldflags="$ADDI_LDFLAGS" \
$ADDITIONAL_CONFIGURE_FLAG
make clean
make
make install

其中NDK是你自己刚刚配置的ndk路径，SYSROOT为platforms中的路径，TOOLCHAIN为toolchains里面中的路径，依次配置好过后保存并退出。
3.开始编译
chmod 777 android_build.sh
./android_build.sh