作者：Sam (甄峰) sam_code@hotmail.com
之前使用过NDK编译过ffmpeg（http://blog.sina.com.cn/s/blog_602f87700102ux7o.html）。这次又要编译新版本ffmpeg. 那次是直接在各模块下添加Android.mk, Application.mk的方式，分别编译各模块。并最终编译出整个版本。
早在ARM-Linux， MIPS-Linux时代，就常用configure 交叉编译ARM或MIPS版本。通常的做法是：
CC=XXX-Linux-gcc LD=XXX-linux-gcc ./configure --host=arm-linux --tegra=.....
接触到Android NDK后，也总觉得可以使用这种方法，而非一定要使用ndk-build 来编译NDK版本的第三方库。但一直没有尝试过。这次在网络上看到RockPlayer编译FFMPEG的方式正是如此。所以干好学习体验之。
在此感谢RockPlayer和相关网友的工作和分享。
思路完全延续RockPlayer, 只针对新版本NDK R9 做了一点点修改：
#!/bin/bash
######################################################
# FFmpeg builds script for Android+ARM platform
#
# This script is released under term of
# CDDL (http://www.opensource.org/licenses/cddl1)
# Wrote by pinxue (~@gmail.com)
from RockPlayer.com
#
2010-8 ~ 2011-4
######################################################
######################################################
# Modify it by sam.zhen (sam_code@hotmail.com)
#
2016-3
######################################################
######################################################
# Usage:
# put this script in top of
FFmpeg source tree
# ./build_android_ffmpeg
#
# It generates binary for following architectures:
#
ARMv6
#
ARMv6+VFP
#
ARMv7+VFPv3-d16 (Tegra2)
#
ARMv7+Neon (Cortex-A8)
#
# Customizing:
# 1. Feel free to change ./configure parameters for more
features
# 2. To adapt other ARM variants
#
set $CPU and $OPTIMIZE_CFLAGS
#
call build_one
######################################################
#SamInfo: MUST modify it for YOUR toolchain path
NDK=/opt/android-ndk-r9
PLATFORM=$NDK/platforms/android-8/arch-arm/
PREBUILT=$NDK/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64
function build_one
{
# -fasm : required. Android header file uses asm keyword instead of
__asm__ , but most of c dialect (like ansi,c99,gnu99) implies
-fno-asm.
#
~/android/android-ndk-r4/build/platforms/android-5/arch-arm//usr/include/asm/byteorder.h:
In function '___arch__swab32':
#
~/android/android-ndk-r4/build/platforms/android-5/arch-arm//usr/include/asm/byteorder.h:25:
error: expected ')' before ':' token
# -fno-short-enums : optimized. Else FFmpeg
obj will generate a huge number of warning for variable-size
enums,
# though we may suppress them
by --no-enum-size-warning, it would be better to avoid it.
# .../ld: warning: cmdutils.o
uses variable-size enums yet the output is to use 32-bit enums; use
of enum values across objects may fail
# --extra-libs="-lgcc" : required. Else cannot solve some runtime
function symbols
# ... undefined reference to
`__aeabi_f2uiz'
# --enable-protocols : required. Without this option, the file
open always fails mysteriously.
# FFmpeg's av_open_input_file
will invoke file format probing functions, but because most of
useful demuxers has flag of zero
# which cause them are ignored
during file format probling and fall to url stream parsing,
# if protocols are disabled,
the file:// url cannot be opened as well.
# $PREBUILT/bin/arm-eabi-ar d libavcodec/libavcodec.a inverse.o
: required.
# FFmpeg includes two copies of
inverse.c both in libavutil and libavcodec for performance
consideration (not sure the benifit yet)
# Without this step, final ld
of generating libffmpeg.so will fail silently, if invoke ld through
gcc, gcc will collect more reasonable error message.
# -llog: debug only, FFmpeg itself doesn't require it at
all.
# With this option, we may
simply includes "utils/Log.h" and use LOGx() to observe FFmpeg's
behavior
# PS, it seems the toolchain
implies -DNDEBUG somewhere, it would be safer to use following
syntax
# #ifdef
NDEBUG
#
#undef NDEBUG
#
#define HAVE_NDEBUG
#
#endif
# #include
"utils/Log.h"
# #ifdef
HAVE_NDEBUG
#
#define NDEBUG
#
#undef HAVE_NDEBUG
# #endif
# --whole-archive : required. Else ld generate a small .so file (about 15k)
# --no-stdlib : required. Android doesn't use standard c runtime but invited its own wheal (bionic libc) because of license consideration.
# space before \ of configure lines: required for some options. Else next line will be merged into previous lines's content and cause problem.
# Especially the --extra-cflags, the next line will pass to gcc in this case and configure will say gcc cannot create executable.
# many options mentioned by articles over internet are implied by -O2 or -O3 already, need not repeat at all.
# two or three common optimization cflags are omitted because not sure about the trade off yet. invoke NDK build system with V=1 to find them.
# -Wl,-T,$PREBUILT/arm-eabi/lib/ldscripts/armelf.x mentioned by almost every articles over internet, but it is not required to specify at all.
# -Dipv6mr_interface=ipv6mr_ifindex : required. Android inet header doesn't use ipv6mr_interface which is required by rfc, seems it generate this user space header file directly from kernel header file, but Linux kernel has decided to keep its own name for ever and ask user space header to use rfc name.
# HAVE_SYS_UIO_H : required. Else:
# In file included from ~/android/android-ndk-r4/build/platforms/android-5/arch-arm//usr/include/linux/socket.h:29,
# from ~/android/android-ndk-r4/build/platforms/android-5/arch-arm//usr/include/sys/socket.h:33,
# from libavformat/network.h:35,
# from libavformat/utils.c:46:
#~/android/android-ndk-r4/build/platforms/android-5/arch-arm//usr/include/linux/uio.h:19: error: redefinition of 'struct iovec'
#
# --disable-doc : required because of strange bug of toolchain.
./configure --target-os=linux \
--prefix=$PREFIX \
--enable-cross-compile \
--extra-libs="-lgcc" \
--arch=arm
\
--enable-gpl
\
--cc=$PREBUILT/bin/arm-linux-androideabi-gcc \
--cross-prefix=$PREBUILT/bin/arm-linux-androideabi- \
--nm=$PREBUILT/bin/arm-linux-androideabi-nm \
--sysroot=$PLATFORM \
--extra-cflags=" -O3 -fpic -DANDROID -DHAVE_SYS_UIO_H=1
-Dipv6mr_interface=ipv6mr_ifindex -fasm -Wno-psabi
-fno-short-enums -fno-strict-aliasing
-finline-limit=300 $OPTIMIZE_CFLAGS " \
--disable-shared \
--enable-static \
--extra-ldflags="-Wl,-rpath-link=$PLATFORM/usr/lib
-L$PLATFORM/usr/lib -nostdlib -lc -lm -ldl -llog"
\
--enable-parsers \
--enable-encoders \
--enable-decoders \
--enable-muxers \
--enable-demuxers \
--enable-swscale \
--enable-swscale-alpha \
--disable-ffplay \
--disable-ffprobe \
--disable-ffserver \
--enable-network \
--enable-indevs \
--disable-bsfs \
--enable-filters \
--enable-avfilter \
--enable-protocols \
--enable-asm
\
$ADDITIONAL_CONFIGURE_FLAG
#make clean
make
make -j4 install
$PREBUILT/bin/arm-linux-androideabi-ar d libavcodec/libavcodec.a
inverse.o
$PREBUILT/bin/arm-linux-androideabi-ld
-rpath-link=$PLATFORM/usr/lib -L$PLATFORM/usr/lib
-soname libffmpeg.so -shared -nostdlib -Bsymbolic
--whole-archive --no-undefined -o $PREFIX/libffmpeg.so
libavcodec/libavcodec.a libavformat/libavformat.a
libavutil/libavutil.a libavfilter/libavfilter.a
libswscale/libswscale.a libavdevice/libavdevice.a
libswresample/libswresample.a
libpostproc/libpostproc.a -lc -lm -lz -ldl
-llog --dynamic-linker=/system/bin/linker
$PREBUILT/lib/gcc/arm-linux-androideabi/4.8/libgcc.a
}
#arm v6
#CPU=armv6
#OPTIMIZE_CFLAGS="-marm -march=$CPU"
#PREFIX=./android/$CPU
#ADDITIONAL_CONFIGURE_FLAG=
#build_one
#arm v7vfpv3
CPU=armv7-a
OPTIMIZE_CFLAGS="-mfloat-abi=softfp -mfpu=vfpv3-d16 -marm
-march=$CPU "
PREFIX=./android/$CPU
ADDITIONAL_CONFIGURE_FLAG=
build_one
#arm v7vfp
#CPU=armv7-a
#OPTIMIZE_CFLAGS="-mfloat-abi=softfp -mfpu=vfp -marm -march=$CPU
"
#PREFIX=./android/$CPU-vfp
#ADDITIONAL_CONFIGURE_FLAG=
#build_one
#arm v7n
#CPU=armv7-a
#OPTIMIZE_CFLAGS="-mfloat-abi=softfp -mfpu=neon -marm -march=$CPU
-mtune=cortex-a8"
#PREFIX=./android/$CPU
#ADDITIONAL_CONFIGURE_FLAG=--enable-neon
#build_one
#arm v6+vfp
#CPU=armv6
#OPTIMIZE_CFLAGS="-DCMP_HAVE_VFP -mfloat-abi=softfp -mfpu=vfp -marm
-march=$CPU"
#PREFIX=./android/${CPU}_vfp
#ADDITIONAL_CONFIGURE_FLAG=
#build_one
此文件命名为：
build_android_ffmpeg
./build_android_ffmpeg
则最终生成 libffmpeg.so
