我们首先需要到ffempeg官网下载然后进行编译生成相关文件，我们会有以下几个文件

image.png

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我们这时候会发现源文件中很多报错了，这是因为我们没有指定路径，和链接额外的 ffmpeg 的编译.so文件,修改CMakeList.txt文件

# 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 3.4.1)

#set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
#判断编译器类型,如果是gcc编译器,则在编译选项中加入c++11支持
if(CMAKE_COMPILER_IS_GNUCXX)
    set(CMAKE_CXX_FLAGS "-std=c++11 ${CMAKE_CXX_FLAGS}")
    message(STATUS "optional:-std=c++11")
endif(CMAKE_COMPILER_IS_GNUCXX)

#需要引入我们头文件,以这个配置的目录为基准
include_directories(src/main/jniLibs/include)
include_directories(src/main/jniLibs/other)

# 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.
#FFMpeg配置
#FFmpeg配置目录
set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../src/main/jniLibs)

# 编解码(最重要的库)
add_library(
            avcodec
            SHARED
            IMPORTED)
set_target_properties(
            avcodec
            PROPERTIES IMPORTED_LOCATION
            ../../../../src/main/jniLibs/armeabi/libavcodec-56.so)

# 设备信息
add_library(
            avdevice
            SHARED
            IMPORTED)
set_target_properties(
            avdevice
            PROPERTIES IMPORTED_LOCATION
            ../../../../src/main/jniLibs/armeabi/libavdevice-56.so)


# 滤镜特效处理库
add_library(
            avfilter
            SHARED
            IMPORTED)
set_target_properties(
            avfilter
            PROPERTIES IMPORTED_LOCATION
            ../../../../src/main/jniLibs/armeabi/libavfilter-5.so)

# 封装格式处理库
add_library(
            avformat
            SHARED
            IMPORTED)
set_target_properties(
            avformat
            PROPERTIES IMPORTED_LOCATION
            ../../../../src/main/jniLibs/armeabi/libavformat-56.so)

# 工具库(大部分库都需要这个库的支持)
add_library(
            avutil
            SHARED
            IMPORTED)
set_target_properties(
            avutil
            PROPERTIES IMPORTED_LOCATION
            ../../../../src/main/jniLibs/armeabi/libavutil-54.so)


# 后期处理
add_library(
            postproc
            SHARED
            IMPORTED)
set_target_properties(
            postproc
            PROPERTIES IMPORTED_LOCATION
            ../../../../src/main/jniLibs/armeabi/libpostproc-53.so)


# 音频采样数据格式转换库
add_library(
            swresample
            SHARED
            IMPORTED)
set_target_properties(
            swresample
            PROPERTIES IMPORTED_LOCATION
            ../../../../src/main/jniLibs/armeabi/libswresample-1.so)

# 视频像素数据格式转换
add_library(
            swscale
            SHARED
            IMPORTED)
set_target_properties(
            swscale
            PROPERTIES IMPORTED_LOCATION
            ../../../../src/main/jniLibs/armeabi/libswscale-3.so)

add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/native-lib.cpp
            # 编译额外的 C 文件
            src/main/cpp/ffmpeg_filter.c
            src/main/cpp/ffmpeg_mod.c
            src/main/cpp/ffmpeg_opt.c
            src/main/cpp/cmdutils.c
              )

# 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.

target_link_libraries( # Specifies the target library.
               # 链接额外的 ffmpeg 的编译,.so文件
              native-lib avcodec avdevice avfilter avformat avutil postproc swresample swscale

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

build.gradle中需要添加这行代码

    defaultConfig {
        applicationId "com.peakmain.ndk"
        minSdkVersion 15
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ""
                //只生成aremabi
                abiFilters "armeabi"
            }
        }
    }

注意：这里有些人在程序编译的时候会报ABIs [armeabi] are not supported for platform. Supported ABIs are [armeabi-v7a, arm64-v8a, x86, x86_64].的错误,解决办法NDK降级到v16 替换AS里NDK或者修改ndk-bundle路径即可,具体的大家可以看这个博客http://blog.51cto.com/4789781/2116935

添加依赖

 implementation 'com.tbruyelle.rxpermissions2:rxpermissions:0.9.5@aar'
 implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'

VideoCompress视频压缩java类

public class VideoCompress {
    //加载so
    static {
        System.loadLibrary("native-lib");
        // 不需要全部 load 相当于 android 调用其他方法类型，不需要全部 load
    }
    // native ffmpeg 压缩视频
    public native void compressVideo(String[] compressCommand,CompressCallback callback);

    public interface CompressCallback{
        public void onCompress(int current,int total);
    }
}

MainActivity的使用

public class MainActivity extends AppCompatActivity {
    private File mInFile = new File(Environment.getExternalStorageDirectory()+"/视频/", "test.mp4");
    private File mOutFile = new File(Environment.getExternalStorageDirectory()+"/视频/", "out.mp4");

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.e("TAG",mInFile.exists()+"");
        TextView tv = (TextView) findViewById(R.id.sample_text);
        // ffmpeg -i test.mp4 -b:v 1024k out.mp4
        // -b:v 码率是什么？ 码率越高视频越清晰，而且视频越大
        // 1M  1024K
        // test.mp4 需要压缩的视频路径
        // out.mp4 压缩后的路径


    }

    public void compressVideo(View view) {
        RxPermissions rxPermissions = new RxPermissions(this);
        rxPermissions.request(Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                .subscribe(new Consumer<Boolean>() {
                    @Override
                    public void accept(Boolean aBoolean) throws Exception {
                        if (aBoolean) {
                            compressVideo();
                        }
                    }
                });
    }

    private void compressVideo() {
        String[] compressCommand = {"ffmpeg", "-i", mInFile.getAbsolutePath(), "-b:v", "1024k", mOutFile.getAbsolutePath()};

        Observable.just(compressCommand)
                .map(new Function<String[], File>() {
                    @Override
                    public File apply(String[] compressCommand) throws Exception {
                        // 压缩是耗时的，子线程，处理权限
                        VideoCompress videoCompress = new VideoCompress();
                        videoCompress.compressVideo(compressCommand, new VideoCompress.CompressCallback() {
                            @Override
                            public void onCompress(int current, int total) {
                                Log.e("TAG","压缩进度："+current+"/"+total);
                            }
                        });
                        return mOutFile;
                    }
                }).subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer<File>() {
                    @Override
                    public void accept(File file) throws Exception {
                        // 压缩完成
                        Log.e("TAG","压缩完成");
                    }
                });
    }
}

native-lib的代码实现

#include <jni.h>
#include <string>
#include <malloc.h>
#include <android/log.h>

#define TAG "JNI_TAG"
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,TAG,__VA_ARGS__)
extern "C" {
JNIEXPORT void JNICALL
Java_com_peakmain_ndk_VideoCompress_compressVideo(JNIEnv *env, jclass type,
                                                  jobjectArray
                                                  compressCommand, jobject callback);
// 声明方法(实现的方式就是基于命令，windows )
// argc 命令的个数
// char **argv 二维数组
int ffmpegmain(int argc, char **argv, void(call_back)(int, int));
}
static jobject call_back_jobj;
static JNIEnv *mEnv;
//回调函数
void call_back(int current, int total) {
    //LOGE("压缩进度：%d/%d",current,total);
    // 把进度回调出去 对象是 jobject callback
    if(call_back_jobj != NULL && mEnv != NULL){
        jclass j_clazz = mEnv->GetObjectClass(call_back_jobj);
        // javap 命令也能打印
        jmethodID j_mid = mEnv->GetMethodID(j_clazz,"onCompress","(II)V");
        mEnv->CallVoidMethod(call_back_jobj,j_mid,current,total);
    }
};


JNIEXPORT void JNICALL
Java_com_peakmain_ndk_VideoCompress_compressVideo(JNIEnv *env, jclass type,
                                                  jobjectArray compressCommand, jobject callback) {
    call_back_jobj = env->NewGlobalRef(callback);
    mEnv=env;
    //ffmpeg处理视频的压缩
    //aremabi这个里面的so都是用来处理音视频，include都是头文件
    //还有几个没有被打包编译成.so文件，因为这些不算是音视频的处理代码，只是我们现在支持命令(封装)
    //1.获取命令行的个数
    int argc = env->GetArrayLength(compressCommand);
    //2.给char **argv填充数据
    char **argv = (char **) malloc(sizeof(char *) * argc);
    for (int i = 0; i < argc; i++) {
        jstring j_params = (jstring) (env->GetObjectArrayElement(compressCommand, i));
        argv[i] = (char *) (env->GetStringUTFChars(j_params, NULL));
        LOGE("参数:%s", argv[i]);
    }
    //3.调用命令去压缩
    ffmpegmain(argc, argv, call_back);
    //4.释放内存
    for (int i = 0; i < argc; ++i) {
        free(argv[i]);
    }
    free(argv);
    env->DeleteGlobalRef(call_back_jobj);
}

注意：我们源码中是没有回调方法的，这时候我们需要修改下ffempeg_mode.c源码

int ffmpegmain(int argc, char **argv,void(call_back)(int,int))
{
if (transcode(call_back) < 0){   
     ffmpeg_cleanup(1);  return 1;}
}

static int transcode(void(call_back)(int,int)){
  print_report(0, timer_start, cur_time,call_back);
}

static void print_report(int is_last_report, int64_t timer_start, int64_t cur_time,void(call_back)(int,int))
{
   // __android_log_print(ANDROID_LOG_ERROR,"TAG","当前帧：%d",frame_number);
            int total_frame_number = input_files[0]->ctx->streams[0]->nb_frames;
            call_back(frame_number,total_frame_number);
}

为了方便知道在哪里添加这行，我截了图

image.png