1 FFmpeg4Android：AS中使用NDK

1.1 用Android.mk编译.so

step 1：创建AS项目MyDNK，新建JNIS类并写好native方法helloJNI()，如图：

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step 2： 进入java文件夹，使用"javah com.lzp.myndk.JNIS"命令，生成头文件：

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step 3：编写test.c文件，实现helloJNI()函数：

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step 4：修改build.gradle文件：

import org.apache.tools.ant.taskdefs.condition.Os

apply plugin: 'com.android.application'

android {

    ...

    //（1）指定动态库路径
    sourceSets{
        main{
            jni.srcDirs = []    // disable automatic ndk-build call, which ignore our Android.mk
            jniLibs.srcDir 'src/main/libs'
        }
    }

    // （2）call regular ndk-build(.cmd) script from app directory
    task ndkBuild(type: Exec) {
        workingDir file('src/main')
        commandLine getNdkBuildCmd()
        //commandLine 'E:/Android/android-ndk-r10e/ndk-build.cmd' //也可以直接使用绝对路径
    }

    tasks.withType(JavaCompile) {
        compileTask -> compileTask.dependsOn ndkBuild
    }

    task cleanNative(type: Exec) {
        workingDir file('src/main')
        commandLine getNdkBuildCmd(), 'clean'
    }

    clean.dependsOn cleanNative
}
//根据不同系统获取ndk-build脚本
def getNdkBuildCmd() {
    def ndkbuild = getNdkDir() + "/ndk-build"
    if (Os.isFamily(Os.FAMILY_WINDOWS))
        ndkbuild += ".cmd"
    return ndkbuild
}
//获取NDK目录路径
def getNdkDir() {
    if (System.env.ANDROID_NDK_ROOT != null)
        return System.env.ANDROID_NDK_ROOT

    Properties properties = new Properties()
    properties.load(project.rootProject.file('local.properties').newDataInputStream())
    def ndkdir = properties.getProperty('ndk.dir', null)
    if (ndkdir == null)
        throw new GradleException("NDK location not found. Define location with ndk.dir in the local.properties file or with an ANDROID_NDK_ROOT environment variable.")
    return ndkdir
}

...

step 6：编译.so文件，有两种方式：
（1）使用ndk-build命令：
进入app\src\main，在cmd中执行NDK的ndk-build命令生成动态库（ndk-build所在文件夹，即NDK目录如果没有加入环境变量则需要绝对路径）；

（2）使用编译脚本（推荐）：
编写Android.mk和Application.mk
Android.mk：

# Android.mk
# walker lee
# http://blog.csdn.net/itismelzp
LOCAL_PATH := $(call my-dir)

# Program
include $(CLEAR_VARS)
LOCAL_MODULE := jni-native  # 库文件，对应生成libjni-native.so文件
LOCAL_SRC_FILES :=test.c    # 还可添加其他.c文件
LOCAL_C_INCLUDES += $(LOCAL_PATH)/include
LOCAL_LDLIBS := -llog -lz
include $(BUILD_SHARED_LIBRARY)

Application.mk：

APP_ABI :=armeabi
APP_PLATFORM := android-9

点击工具栏中的build->Make Project，会在main目录下生成两个目录libs和obj，动态库便在其中：

image.png

1.2 用CMakeList编译.so

step 1：新建CMakeLists.txt文件：

# Sets the minimum version of CMake required to build the native
# library. You should either keep the default value or only pass a
# value of 3.4.0 or lower.

cmake_minimum_required(VERSION 3.4.1)

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 )

add_library( jni-native
             SHARED
             src/main/jni/test.c )

include_directories(jni)

#target_include_directories(jni-native PRIVATE jni)

target_link_libraries( jni-native
                       ${log-lib} )