macOS上編譯android的ffmpeg及ffmpeg.c

?1 前言

? ? 前段時間介紹過使用xcode和qt creator編譯調試ffmepg.c，運行平臺是在macOS上，本文擬介紹下android平臺如何用NDK編譯鏈編譯ffmepg庫并使用。

macOS上使用qt creator編譯調試ffmpeg.c

macOS上將ffmpeg.c編譯成Framework

? ? 大體思路：

其一，分別介紹使用GCC和CLang編譯器來編譯ffmpeg庫的方法；
其二，介紹如何將ffmpeg的多個.a庫打包成1個so庫之法；
其三，使用android studio新建一個native c++ Library工程，并將ffmepg庫引入到工程使用；

2 下載FFmpeg源碼

? ? 首先從git倉庫將ffmpeg代碼下載到本地：

git clone https://github.com/FFmpeg/FFmpeg.git && git checkout release/6.1

3 編譯FFmpeg

3.1 GCC編譯

? ? 編譯環境：

ffmpeg release/6.1分支
android ndk?17.2.4988734版本，可借助android studio工具下載;

? ? 通過給編譯腳本傳參(aarch64/x86_64)支持arm64和x86_64架構：??

#! /usr/bin/env bashset -eARG_COUNT=$#
#支持架構aarch64 x86_64
ARCH_NAME=$1
if [[ ${ARG_COUNT} -lt 1 ]]||[[ ${ARCH_NAME} != "aarch64" && ${ARCH_NAME} != "x86_64" ]]; thenecho "Usage:./build_ffmpeg_for_android.sh aarch64/x86_64"exit -1
fiNDK_ROOT=/Users/mingo/Library/Android/sdk/ndk/17.2.4988734
SYSROOT=${NDK_ROOT}/sysroot
echo "ARCH_NAME=${ARCH_NAME}"
TOOLCHAIN_ARCH=${ARCH_NAME}-linux-android
FLATFORM=${NDK_ROOT}/platforms/android-28/arch-arm64
SYSROOT_INCLUDE_PATH="-I${SYSROOT}/usr/include/${ARCH_NAME}-linux-android -isysroot ${SYSROOT}"
COMPILER_PREFIX=${ARCH_NAME}-linux-android
CURRENT_DIR=`pwd`
BUILD_OUTPUT_DIR="${CURRENT_DIR}/android/arm64"
if [ ${ARCH_NAME} == "x86_64" ]; thenTOOLCHAIN_ARCH=${ARCH_NAME}FLATFORM=${NDK_ROOT}/platforms/android-28/arch-x86_64BUILD_OUTPUT_DIR="${CURRENT_DIR}/android/x86_64"
fi
if [ ! -d ${BUILD_OUTPUT_DIR} ]; thenmkdir -p ${BUILD_OUTPUT_DIR}
fi
echo "TOOLCHAIN_RCH=${TOOLCHAIN_ARCH}"
PREBUILT=${NDK_ROOT}/toolchains/${TOOLCHAIN_ARCH}-4.9/prebuilt/darwin-x86_64/binFF_CFLAGS="-O3 -Wall -pipe -std=c11 -ffast-math -fstrict-aliasing -Werror=strict-aliasing -Wno-psabi -Wa,--noexecstack -DANDROID -DDEBUG"
FF_CXXFLAGS="-D__thumb__ -fexceptions -frtti"function build_for() {echo "start to configure ffmpeg"./configure --prefix=${BUILD_OUTPUT_DIR} \--sysroot=${FLATFORM} \--cross-prefix=${PREBUILT}/${COMPILER_PREFIX}- \--cc=${PREBUILT}/${COMPILER_PREFIX}-gcc \--enable-cross-compile --arch=${ARCH_NAME} --target-os=android \--enable-shared \--enable-pic \--disable-symver \--disable-asm \--enable-inline-asm \--disable-optimizations \--enable-debug \--disable-small \--disable-ffmpeg \--disable-ffprobe \--disable-ffplay \--disable-doc \--extra-cflags="${SYSROOT_INCLUDE_PATH} ${FFLAGS}" \--extra-cxxflags="${FF_CXXFLAGS}" \--extra-ldflags="-L${FLATFORM}/usr/lib"make cleanmake -j9make install
}build_forif [ $? -eq 0 ]; thenecho "configure ffmpeg succ"
elseecho "configure ffmpeg fail"
fi

? ? ?起初所用NDK版本是16.1.4479499版本，遇到編譯問題：

? ? 通過將NDK版本升級到17.2.4988734解決：

? ? ?NDK的android api選擇android-28：

xxxxx@localhost:~/Library/Android/sdk/ndk/17.2.4988734/platforms$tree -L 1
.
├── NOTICE
├── android-14
├── android-15
├── android-16
├── android-17
├── android-18
├── android-19
├── android-21
├── android-22
├── android-23
├── android-24
├── android-26
├── android-27
├── android-28
└── repo.prop14 directories, 2 files

? ? 將shell腳本改成如下即可：?

NDK_ROOT=/Users/xxx/Library/Android/sdk/ndk/17.2.4988734FLATFORM=${NDK_ROOT}/platforms/android-28/arch-arm64--extra-ldflags="-L${FLATFORM}/usr/lib"

? ? ?然后執行編譯安裝：

sh build_for_android.sh aarch64(或x86_64)

arm64平臺編譯后輸出目錄在ffmpeg的根目錄下android/arm64目錄；
x86_64平臺編譯后輸出目錄在ffmpeg的根目錄下的android/x86_64目錄；?

? ? 執行腳本命令之后，可編譯成功：?

3.2 使用ffmpeg庫

? ? CMakeLists腳本如下：

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html# Sets the minimum version of CMake required to build the native library.cmake_minimum_required(VERSION 3.22.1)# Declares and names the project.project("ndkffmpeg")# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.add_library( # Sets the name of the library.ndkffmpeg# Sets the library as a shared library.SHARED# Provides a relative path to your source file(s).native-lib.cpp)# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.find_library( # Sets the name of the path variable.log-lib# Specifies the name of the NDK library that# you want CMake to locate.log)# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.set(FFMPEG_ROOT_DIR ${CMAKE_CURRENT_SOURCE_DIR}/../jniLibs)
set(FFMPEG_INCLUDE_DIR ${FFMPEG_ROOT_DIR}/include)
set(FFMPEG_LIB_DIR ${FFMPEG_ROOT_DIR}/${ANDROID_ABI})#導入ffmpeg相關依賴庫
list(APPEND DEPENDCY_LIB_LIST avutil avformat avcodec avfilter avdevice swscale swresample)
list(APPEND DEPENDCY_LIB_LIST ffmpeg)
foreach(libname IN LISTS DEPENDCY_LIB_LIST)add_library(${libname} SHARED IMPORTED)set_target_properties( ${libname} PROPERTIES IMPORTED_LOCATION  ${FFMPEG_LIB_DIR}/lib${libname}.so)
endforeach()include_directories(${FFMPEG_INCLUDE_DIR} ${FFMPEG_ROOT_DIR}/../)
target_link_directories(ndkffmpeg PRIVATE ${FFMPEG_LIB_DIR})# 設置庫文件的輸出路徑
set_target_properties(ndkffmpeg PROPERTIESLIBRARY_OUTPUT_DIRECTORY ${FFMPEG_LIB_DIR}ARCHIVE_OUTPUT_DIRECTORY ${FFMPEG_LIB_DIR})
target_link_libraries( # Specifies the target library.ndkffmpegavutilavformatavcodecavfilteravdeviceswresampleswscale# Links the target library to the log library# included in the NDK.${log-lib})

? ? 在編寫完成CMakeLists腳本后，并且在工程目錄下引入so和include文件：

? ? 在native-lib.cpp里寫一個簡單的程序看看效果：?

#include <jni.h>
#include <string>extern "C" {
#include "libavformat/avformat.h"
}static int decode_interrupt_cb(void *ctx) {return 0;
}static void test_ffmpeg_func() {AVFormatContext* ifmt = NULL;const char* filename = "rtmp://10.0.2.2/live/8";AVDictionary *d = NULL;//av_dict_set(&d, "timeout", NULL, 0);//av_dict_set(&d, "fflags", "nobuffer", 0);int ret = avformat_open_input(&ifmt, filename, NULL, &d);ret = avformat_find_stream_info(ifmt, NULL);AVPacket pkt;av_init_packet(&pkt);while (1) {int ret = av_read_frame(ifmt, &pkt);if (ret < 0) {av_log(NULL, AV_LOG_INFO, "error\n");}if (pkt.stream_index == AVMEDIA_TYPE_VIDEO && pkt.flags & AV_PKT_FLAG_KEY) {//av_log(NULL, AV_LOG_INFO, "keyframe\n");}}
}extern "C" JNIEXPORT jstring JNICALL
Java_com_example_ndkffmpeg_MainActivity_stringFromJNI(JNIEnv* env,jobject /* this */) {av_log_set_level(AV_LOG_DEBUG);test_ffmpeg_func();std::string hello = "Hello from C++";return env->NewStringUTF(hello.c_str());
}

? ? 調試運行效果；?

? ? 可以看到，app已經成功將ffmpeg各庫加載起來，并可使用了。?

?3.3 Clang編譯

? ? 以上是GCC編譯器編譯ffmpeg，此處再介紹使用clang編譯器來編譯ffmpeg，編譯環境：

ffmpeg release/6.1版本；
android ndk?21.3.6528147版本；

? ? 支持arm64和x86_64架構：?

#! /usr/bin/env bashset -eARG_COUNT=$#
#支持架構aarch64 x86_64
ARCH_NAME=$1
if [[ ${ARG_COUNT} -lt 1 ]]||[[ ${ARCH_NAME} != "aarch64" && ${ARCH_NAME} != "x86_64" ]]; thenecho "Usage:./build_ffmpeg_for_android.sh aarch64/x86_64"exit -1
fiNDK_ROOT=/Users/mingo/Library/Android/sdk/ndk/21.3.6528147
ANDROID_VER=28
FLATFORM=${NDK_ROOT}/platforms/android-${ANDROID_VER}/arch-arm64
ENABLE_OPT="--enable-asm"
CURRENT_DIR=`pwd`
OUTPUT_DIR="${CURRENT_DIR}/android_clang/arm64"
if [ ${ARCH_NAME} == "x86_64" ]; thenFLATFORM=${NDK_ROOT}/platforms/android-${ANDROID_VER}/arch-x86_64ENABLE_OPT="--disable-asm"OUTPUT_DIR="${CURRENT_DIR}/android_clang/x86_64"
fi
if [ ! -d ${OUTPUT_DIR} ]; thenmkdir -p ${OUTPUT_DIR}
fi
PREBUILT=${NDK_ROOT}/toolchains/llvm/prebuilt/darwin-x86_64/bin
COMPILER_PREFIX=${ARCH_NAME}-linux-android
SYSROOT=${PREBUILT}/../sysrootFF_CFLAGS="-O3 -Wall -pipe -std=c11 -ffast-math -fstrict-aliasing -Werror=strict-aliasing -Wno-psabi -Wa,--noexecstack -DANDROID -DDEBUG"
FF_CXXFLAGS="-D__thumb__ -fexceptions -frtti"function build_for() {echo "start to configure ffmpeg"./configure --prefix=${OUTPUT_DIR} \--sysroot=${SYSROOT} \--cross-prefix=${PREBUILT}/${COMPILER_PREFIX}- \--cc=${PREBUILT}/${COMPILER_PREFIX}${ANDROID_VER}-clang \--cxx=${PREBUILT}/${COMPILER_PREFIX}${ANDROID_VER}-clang++ \--enable-cross-compile --arch=${ARCH_NAME} --target-os=android \--enable-shared \--enable-pic \--disable-symver \${ENABLE_OPT} \--enable-inline-asm \--disable-optimizations \--enable-debug \--disable-small \--disable-ffmpeg \--disable-ffprobe \--disable-ffplay \--disable-doc \--extra-cflags="${FFLAGS}"\--extra-cxxflags="${FF_CXXFLAGS}" \--extra-ldflags="-L${FLATFORM}/usr/lib"make cleanmake -j9make install
}build_forif [ $? -eq 0 ]; thenecho "configure ffmpeg succ"
elseecho "configure ffmpeg fail"
fi

? ? 然后，通過在命令行執行如下命令編譯，編譯arm64架構的：?

sh build_ffmpeg_for_android_with_clang.sh aarch64

? ? 編譯x86_64架構的：?

sh build_ffmpeg_for_android_with_clang.sh x86_64

? ? ?編譯的輸出目錄在ffmpeg的目錄下：

arm64輸出在ffmpeg根目錄下android_clang/arm64目錄;
x86_64輸出在ffmpeg的根目錄下的android_clang/x86_64下；

? ? 提示：clang編譯僅做介紹，后續ffmpeg.c的編譯仍將使用NDK?17.2.4988734版本和GCC編譯器。

3.4 多個.a庫打包成1個so

將libavutil libavformat libavcodec libavfilter libavdevice libswsample libswscale幾個.a庫打包成一個so庫；
*.a? =>? libffmpeg.so

? ? 主要思路：

configure的時候配置只編譯生成ffmpeg的static庫，而放棄編譯shared庫；
用交叉編譯鏈中的鏈接器將ffmpeg的相關.a庫鏈接成1個so庫；

? ? 貼出編譯&打包的shell腳本：

#! /usr/bin/env bashset -eARG_COUNT=$#
#支持架構aarch64 x86_64
ARCH_NAME=$1
if [[ ${ARG_COUNT} -lt 1 ]]||[[ ${ARCH_NAME} != "aarch64" && ${ARCH_NAME} != "x86_64" ]]; thenecho "Usage:./build_ffmpeg_for_android.sh aarch64/x86_64"exit -1
fiNDK_ROOT=/Users/mingo/Library/Android/sdk/ndk/17.2.4988734
SYSROOT=${NDK_ROOT}/sysroot
echo "ARCH_NAME=${ARCH_NAME}"
TOOLCHAIN_ARCH=${ARCH_NAME}-linux-android
FLATFORM=${NDK_ROOT}/platforms/android-28/arch-arm64
echo "FLATFORM=${FLATFORM}"
SYSROOT_INCLUDE_PATH="-I${SYSROOT}/usr/include/${ARCH_NAME}-linux-android -isysroot ${SYSROOT}"
COMPILER_PREFIX=${ARCH_NAME}-linux-android
CURRENT_DIR=`pwd`
BUILD_OUTPUT_DIR="${CURRENT_DIR}/android/arm64"
if [ ${ARCH_NAME} == "x86_64" ]; thenTOOLCHAIN_ARCH=${ARCH_NAME}FLATFORM=${NDK_ROOT}/platforms/android-28/arch-x86_64BUILD_OUTPUT_DIR="${CURRENT_DIR}/android/x86_64"
fi
if [ ! -d ${BUILD_OUTPUT_DIR} ]; thenmkdir -p ${BUILD_OUTPUT_DIR}
fi
echo "TOOLCHAIN_RCH=${TOOLCHAIN_ARCH}"
PREBUILT=${NDK_ROOT}/toolchains/${TOOLCHAIN_ARCH}-4.9/prebuilt/darwin-x86_64/binFF_CFLAGS="-O3 -Wall -pipe -fpic -std=c11 -ffast-math -fstrict-aliasing -Werror=strict-aliasing -Wno-psabi -Wa,--noexecstack -DANDROID -DDEBUG"
FF_CXXFLAGS="-D__thumb__ -fexceptions -frtti"
FF_LDFLAGS="-lc -ldl -lm -lz -llog -lgcc"function build_for() {echo "start to configure ffmpeg"./configure --prefix=${BUILD_OUTPUT_DIR} \--sysroot=${FLATFORM} \--cross-prefix=${PREBUILT}/${COMPILER_PREFIX}- \--cc=${PREBUILT}/${COMPILER_PREFIX}-gcc \--enable-cross-compile --arch=${ARCH_NAME} --target-os=android \--disable-shared \--enable-static \--disable-optimizations \--enable-debug \--disable-small \--disable-ffmpeg \--disable-ffprobe \--disable-ffplay \--disable-doc \--extra-cflags="${SYSROOT_INCLUDE_PATH} ${FFLAGS}" \--extra-cxxflags="${FF_CXXFLAGS}" \--extra-ldflags="${FF_LDFLAGS} -L${FLATFORM}/usr/lib"make cleanmake -j9make install
}build_forif [ $? -eq 0 ]; thenecho "configure ffmpeg succ"
elseecho "configure ffmpeg fail"
fiGCC_PREFIX=${PREBUILT}/../lib/gcc/${COMPILER_PREFIX}/4.9.x
RPATH=${FLATFORM}/usr/lib
if [ ${ARCH_NAME} == "x86_64" ]; thenRPATH=${FLATFORM}/usr/lib64
fi
echo "RPATH=${RPATH}"
package_ffmpeg_libs() {${PREBUILT}/${COMPILER_PREFIX}-ld -L${BUILD_OUTPUT_DIR}/lib -L${GCC_PREFIX} -L${RPATH} \-rpath-link=${RPATH} -L${RPATH} -soname libffmpeg.so \-shared -nostdlib -Bsymbolic --whole-archive --no-undefined -o ${BUILD_OUTPUT_DIR}/lib/libffmpeg.so \-lavformat -lavcodec -lavfilter -lavdevice -lswresample -lswscale -lavutil -lgcc \-lcamera2ndk -lmediandk -lnativewindow \-lc -ldl -lm -lz -llog \--dynamic-linker=/system/bin/linker# 設置動態鏈接器，不同平臺的不同，android 使用的是/system/bin/linker
}package_ffmpeg_libsif [ $? -eq 0 ]; thenecho "package ffmpeg succ"
elseecho "package ffmpeg fail"
fi

? ? 遇到1個問題:

/Users/xxx/Applications/workspace/FFmpeg/android/arm64/lib/libswscale.a(half2float.o): In function `ff_init_half2float_tables':
/Users/xxx/Applications/workspace/FFmpeg/./libavutil/half2float.c:40: multiple definition of `ff_init_half2float_tables'
/Users/xxx/Applications/workspace/FFmpeg/android/arm64/lib/libavcodec.a(half2float.o):/Users/mingo/Applications/workspace/FFmpeg/./libavutil/half2float.c:40: first defined here

? ? 問題原因：

上述問題的原因是libavcodec.a庫和libswscale.a庫均打包了half2float.o文件；
在將上述庫最終鏈接打包成同一個so的時候就會出現上述重復定義問題；

? ? 解決辦法：

打開libswscale/Makefile文件，將half2float.o文件去掉，libswscale不打包該文件，只讓libavcodec打包該文件；?

? ? 打包后的libffmpeg.so輸出在以下目錄，成功將ffmpeg相關.a庫打包成libffmpeg.so庫：?

mingo@localhost:~/Applications/workspace/FFmpeg/android$tree -L 3
.
└── arm64├── include│?? ├── libavcodec│?? ├── libavdevice│?? ├── libavfilter│?? ├── libavformat│?? ├── libavutil│?? ├── libswresample│?? └── libswscale├── lib│?? ├── libavcodec.a│?? ├── libavdevice.a│?? ├── libavfilter.a│?? ├── libavformat.a│?? ├── libavutil.a│?? ├── libffmpeg.so│?? ├── libswresample.a│?? ├── libswscale.a│?? └── pkgconfig└── share└── ffmpeg14 directories, 8 files

?4 使用libffmpeg.so

? ? 使用android studio新建一個native c++ Library工程：

在main目錄下新建jniLibs目錄，將libffmpeg.so庫放到arm64-v8a子目錄下；
ffmpeg相關頭文件放到jniLibs目錄下的include子目錄下；

? ? 在app的build.gradle文件下增加abiFilters：

android {namespace 'com.example.ndkffmpeg'compileSdk 33defaultConfig {applicationId "com.example.ndkffmpeg"minSdk 24targetSdk 33versionCode 1versionName "1.0"testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"ndk {// 其他x86_64按此添加，逗號分割abiFilters 'arm64-v8a'}externalNativeBuild {cmake {cppFlags '-std=c++11'}}}
}

? ? ?貼出所寫CMakeLists腳本：

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html# Sets the minimum version of CMake required to build the native library.cmake_minimum_required(VERSION 3.22.1)# Declares and names the project.project("ndkffmpeg")# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.add_library( # Sets the name of the library.ndkffmpeg# Sets the library as a shared library.SHARED# Provides a relative path to your source file(s).native-lib.cpp)# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.find_library( # Sets the name of the path variable.log-lib# Specifies the name of the NDK library that# you want CMake to locate.log)# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.set(FFMPEG_ROOT_DIR ${CMAKE_CURRENT_SOURCE_DIR}/../jniLibs)
set(FFMPEG_INCLUDE_DIR ${FFMPEG_ROOT_DIR}/include)
set(FFMPEG_LIB_DIR ${FFMPEG_ROOT_DIR}/${ANDROID_ABI})include_directories(${FFMPEG_INCLUDE_DIR} ${FFMPEG_ROOT_DIR}/../)
target_link_directories(ndkffmpeg PRIVATE ${FFMPEG_LIB_DIR})# 設置庫文件的輸出路徑
set_target_properties(ndkffmpeg PROPERTIESLIBRARY_OUTPUT_DIRECTORY ${FFMPEG_LIB_DIR}ARCHIVE_OUTPUT_DIRECTORY ${FFMPEG_LIB_DIR})
target_link_libraries( # Specifies the target library.ndkffmpegffmpeg# Links the target library to the log library# included in the NDK.${log-lib})

? ? 在AndroidManifest.xml文件中請求網絡訪問權限：?

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/><uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /><uses-permission android:name="android.permission.READ_PHONE_STATE" /><uses-permission android:name="android.permission.INTERNET" /><uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /><applicationandroid:allowBackup="true"android:dataExtractionRules="@xml/data_extraction_rules"android:fullBackupContent="@xml/backup_rules"android:icon="@mipmap/ic_launcher"android:label="@string/app_name"android:roundIcon="@mipmap/ic_launcher_round"android:supportsRtl="true"android:theme="@style/Theme.MyApplication"tools:targetApi="31"><activityandroid:name=".MainActivity"android:exported="true"><intent-filter><action android:name="android.intent.action.MAIN" /><category android:name="android.intent.category.LAUNCHER" /></intent-filter></activity></application></manifest>

? ? native-lib.cpp代碼貼出:

#include <jni.h>
#include <string>extern "C" {
#include "libavformat/avformat.h"
}static int decode_interrupt_cb(void *ctx) {return 0;
}static void test_ffmpeg_func() {AVFormatContext* ifmt = NULL;const char* filename = "rtmp://10.0.2.2/live/8";AVDictionary *d = NULL;//av_dict_set(&d, "timeout", NULL, 0);//av_dict_set(&d, "fflags", "nobuffer", 0);int ret = avformat_open_input(&ifmt, filename, NULL, &d);ret = avformat_find_stream_info(ifmt, NULL);AVPacket pkt;av_init_packet(&pkt);while (1) {int ret = av_read_frame(ifmt, &pkt);if (ret < 0) {av_log(NULL, AV_LOG_INFO, "error\n");}if (pkt.stream_index == AVMEDIA_TYPE_VIDEO && pkt.flags & AV_PKT_FLAG_KEY) {//av_log(NULL, AV_LOG_INFO, "keyframe\n");}}
}extern "C" JNIEXPORT jstring JNICALL
Java_com_example_ndkffmpeg_MainActivity_stringFromJNI(JNIEnv* env,jobject /* this */) {av_log_set_level(AV_LOG_DEBUG);test_ffmpeg_func();std::string hello = "Hello from C++";return env->NewStringUTF(hello.c_str());
}

? ? ?輸入正確的filename地址即調試運行：

5 編譯ffmpeg.c為so

? ? 編譯環境如下：

ffmpeg release/6.1
NDK?17.2.4988734;

? ? 首先進入到ffmpeg源碼目錄下的fftools子目錄，即為編譯ffmpeg命令行程序的工作目錄：

xxx@localhost:~/Applications/workspace/FFmpeg/fftools$tree -L 1
.
├── Makefile
├── build_ffmpeg_for_android.sh
├── cmdutils.c
├── cmdutils.h
├── ffmpeg.c
├── ffmpeg.h
├── ffmpeg_dec.c
├── ffmpeg_demux.c
├── ffmpeg_enc.c
├── ffmpeg_filter.c
├── ffmpeg_hw.c
├── ffmpeg_mux.c
├── ffmpeg_mux.h
├── ffmpeg_mux_init.c
├── ffmpeg_opt.c
├── ffplay.c
├── ffprobe.c
├── fftools.manifest
├── fftoolsres.rc
├── fopen_utf8.h
├── objpool.c
├── objpool.h
├── opt_common.c
├── opt_common.h
├── sync_queue.c
├── sync_queue.h
├── thread_queue.c
└── thread_queue.h1 directory, 28 files

5.1 改寫ffmpeg接口名

? ? 將ffmpeg命令行程序的main方法名改寫為ffmpeg名。頭文件和.c文件都需要修改：

int ffmpeg(int argc, char* argv[])

?5.1 工作目錄

? ? 在此列出主要工作目錄和fftools目錄結構及輸出目錄接口，其他目錄結構忽略掉：

├── CONTRIBUTING.md
├── COPYING.GPLv2
├── COPYING.GPLv3
├── COPYING.LGPLv2.1
├── COPYING.LGPLv3
├── CREDITS
├── Changelog
├── INSTALL.md
├── LICENSE.md
├── MAINTAINERS
├── Makefile
├── README.md
├── RELEASE
├── RELEASE_NOTES
├── android_arm64_output
│?? ├── include
│?? ├── lib
│?? └── share
├── android_x86_64_output
│?? ├── include
│?? ├── lib
│?? └── share
├── build_ffmpeg_for_android.sh
├── build_ffmpeg_for_android_with_clang.sh
├── config.h
├── config_components.h
├── configure
├── fftools
│?? ├── Makefile
│?? ├── build_ffmpeg_for_android.sh
│?? ├── cmdutils.c
│?? ├── cmdutils.h
│?? ├── ffmpeg.c
│?? ├── ffmpeg.h
│?? ├── ffmpeg_dec.c
│?? ├── ffmpeg_demux.c
│?? ├── ffmpeg_enc.c
│?? ├── ffmpeg_filter.c
│?? ├── ffmpeg_hw.c
│?? ├── ffmpeg_mux.c
│?? ├── ffmpeg_mux.h
│?? ├── ffmpeg_mux_init.c
│?? ├── ffmpeg_opt.c
│?? ├── ffplay.c
│?? ├── ffprobe.c
│?? ├── fftools.manifest
│?? ├── fftoolsres.rc
│?? ├── fopen_utf8.h
│?? ├── objpool.c
│?? ├── objpool.h
│?? ├── opt_common.c
│?? ├── opt_common.h
│?? ├── sync_queue.c
│?? ├── sync_queue.h
│?? ├── thread_queue.c
│?? └── thread_queue.h

5.2 GCC編譯

? ? 編寫shell腳本，放在fftools目錄下，使用GCC編譯ffmepg命令行程序為so庫，腳本如下，支持arm64和x86_64架構：

#! /usr/bin/env bashset -eARG_COUNT=$#
#支持架構aarch64 x86_64
ARCH_NAME=$1
if [[ ${ARG_COUNT} -lt 1 ]]||[[ ${ARCH_NAME} != "aarch64" && ${ARCH_NAME} != "x86_64" ]]; thenecho "Usage:./build_ffmpeg_for_android.sh aarch64/x86_64"exit -1
fi
echo "ARCH_NAME=${ARCH_NAME}"NDK_ROOT=/Users/mingo/Library/Android/sdk/ndk/17.2.4988734
SYSROOT=${NDK_ROOT}/sysroot
TOOLCHAIN_ARCH=${ARCH_NAME}-linux-android
FLATFORM=${NDK_ROOT}/platforms/android-28/arch-arm64
SYSROOT_INCLUDE_PATH="${SYSROOT}/usr/include/${ARCH_NAME}-linux-android -isysroot ${SYSROOT}"
COMPILER_PREFIX=${ARCH_NAME}-linux-android
CURRENT_DIR=`pwd`
BUILD_OUTPUT_DIR="${CURRENT_DIR}/../android/arm64"
if [ ${ARCH_NAME} == "x86_64" ]; thenTOOLCHAIN_ARCH=${ARCH_NAME}FLATFORM=${NDK_ROOT}/platforms/android-28/arch-x86_64BUILD_OUTPUT_DIR="${CURRENT_DIR}/../android/x86_64"
fi
echo "BUILD_OUTPUT_DIR=${BUILD_OUTPUT_DIR}"
if [ ! -d ${BUILD_OUTPUT_DIR} ]; thenmkdir -p ${BUILD_OUTPUT_DIR}
fi
echo "TOOLCHAIN_RCH=${TOOLCHAIN_ARCH}"
PREBUILT=${NDK_ROOT}/toolchains/${TOOLCHAIN_ARCH}-4.9/prebuilt/darwin-x86_64/binFF_CFLAGS="-O3 -Wall -fpic -pipe -std=c11 -ffast-math -fstrict-aliasing -Werror=strict-aliasing -Wno-psabi -Wa,--noexecstack -Wpointer-sign -Wparentheses -DANDROID -DDEBUG"
FF_CXXFLAGS="-D__thumb__ -fexceptions -frtti"CC=${PREBUILT}/${COMPILER_PREFIX}-gcc
FFMPEG_ROOT_DIR=${BUILD_OUTPUT_DIR}
FFMPEG_INCLUDE_DIR=${FFMPEG_ROOT_DIR}/include
FFMPEG_LIB_DIR=${FFMPEG_ROOT_DIR}/lib
CONFIG_H_DIR=${CURRENT_DIR}/../
FFMPEG_LIBS="-lavutil -lavformat -lavcodec -lavfilter -lavdevice -lswresample -lswscale"
ANDROID_MEDIA_LIBS="-lcamera2ndk -lmediandk"function build_for() {echo "compile ffmpeg..."FFMPEG_SRC="cmdutils.c ffmpeg_dec.c ffmpeg_demux.c ffmpeg_enc.c ffmpeg_filter.c \ffmpeg_hw.c ffmpeg_mux_init.c ffmpeg_mux.c ffmpeg_opt.c ffmpeg.c \objpool.c opt_common.c \sync_queue.c thread_queue.c"${CC} --sysroot=${FLATFORM} ${FF_CFLAGS} -shared ${FFMPEG_SRC} -o ${FFMPEG_LIB_DIR}/libffmpegc.so \-I${FFMPEG_INCLUDE_DIR} -I${CONFIG_H_DIR} -I${SYSROOT_INCLUDE_PATH} \-L${FFMPEG_LIB_DIR} -L${PLATFORM}/usr/lib \${FFMPEG_LIBS} ${ANDROID_MEDIA_LIBS}
}build_forif [ $? -eq 0 ]; thenecho "compile ffmpegc succ"
elseecho "compile ffmpegc fail"
fi

? ? 按照以上腳本編譯，可順利完成arm64和x86_64的編譯工作。最后的輸出目錄在：

arm64和_x8664平臺輸出均與對應平臺ffmpeg庫路徑一致；?

? ? 提示：此處編譯ffmpeg.c為so的時候，需要靜態鏈接ffmpeg的各.a庫。?

? ? 然后，使用工具可以看到libffmpegc.so相關so的依賴庫信息：

Dynamic section at offset 0x1c62808 contains 28 entries:Tag        Type                         Name/Value0x0000000000000001 (NEEDED)             Shared library: [libcamera2ndk.so]0x0000000000000001 (NEEDED)             Shared library: [libmediandk.so]0x0000000000000001 (NEEDED)             Shared library: [libc.so]0x0000000000000001 (NEEDED)             Shared library: [libdl.so]0x0000000000000001 (NEEDED)             Shared library: [libm.so]0x0000000000000001 (NEEDED)             Shared library: [libz.so]0x0000000000000001 (NEEDED)             Shared library: [liblog.so]0x000000000000001a (FINI_ARRAY)         0x1b703780x000000000000001c (FINI_ARRAYSZ)       8 (bytes)0x0000000000000004 (HASH)               0x1c80x0000000000000005 (STRTAB)             0x323100x0000000000000006 (SYMTAB)             0xab300x000000000000000a (STRSZ)              137735 (bytes)0x000000000000000b (SYMENT)             24 (bytes)0x0000000000000003 (PLTGOT)             0x1c72a080x0000000000000002 (PLTRELSZ)           73680 (bytes)0x0000000000000014 (PLTREL)             RELA0x0000000000000017 (JMPREL)             0x163c500x0000000000000007 (RELA)               0x572100x0000000000000008 (RELASZ)             1100352 (bytes)0x0000000000000009 (RELAENT)            24 (bytes)0x0000000000000018 (BIND_NOW)0x000000006ffffffb (FLAGS_1)            Flags: NOW0x000000006ffffffe (VERNEED)            0x571c00x000000006fffffff (VERNEEDNUM)         20x000000006ffffff0 (VERSYM)             0x53d180x000000006ffffff9 (RELACOUNT)          403180x0000000000000000 (NULL)               0x0

? ? 所用工具及其執行命令如下：

~/Library/Android/sdk/ndk/21.3.6528147/toolchains/aarch64-linux-android-4.9/prebuilt/darwin-x86_64/bin/aarch64-linux-android-readelf libffmpegc.so -d