Android Studio通过JNI(CMake方式)集成FFMpeg音视频处理框架

前言

本FFMpeg的源码多采用C/C++代码编写的，想要使用FFmpeg提供的库函数，需要将其打包成动态链接库文件。如Linux的so库文件，windows上的dll库文件，Android系统的底层是基于Linux系统内核的，因此要在Android平台上使用FFmpeg框架提供的库函数，需要将其打包成so库文件。而在Linux系统编译打包，需要在FFmpeg框架源码的目录下建立Linux的批文件Shell脚本文件，即可在Linux系统运行命令的脚本文件(Windows系统为bat文件)。本篇博文介绍如何用JNI的方式集成FFmpeg，如果你还了解如何用CMake集成FFmpeg，可以查看 Android CMake集成JNI开发环境和 Android JNI实现Java与C/C++互相调用，以及so库的生成和应用(JNI方式调用美图秀秀so)。有关Android集成FFmpeg框架及其应用的源码在Github上，喜欢给个star，谢谢哦。本人博客会长期更新有关Android FFmpeg,OpenGL和OpenCV,OpenSL。如果您感兴趣的话，可以关注我CSDN哦，博客会持续更新。

本篇文件按如下步骤进行介绍

• windows下编译FFmpeg源码，得到so库文件
• 利用JNI将so库集成到Android项目中
• 通过native方法在C++文件中调用FFmpeg框架的库函数

下面我们看看具体的实现步骤

编译FFmpeg，取得so库文件

windows环境下编译FFmpeg，需要下载如下工具和源码

1. 下载安装MinGW
2. 下载yasm
3. 下载FFMpeg

下载好FFmpeg源码和MinGW工具后，就可以开始编译FFmpeg了

首先需要对源代码中的configure文件进行修改，由于编译出来的动态库文件名的版本号在.so之后(例如 “libavcodec.so.5.100.1”),而Android平台不能识别这样的文件名，所以需要修改这种文件名。找到FFMpeg文件夹下面的configure文件，做如下修改

SLIBNAME_WITH_MAJOR='$(SLIBNAME).$(LIBMAJOR)'
LIB_INSTALL_EXTRA_CMD='$$(RANLIB) "$(LIBDIR)/$(LIBNAME)"'
SLIB_INSTALL_NAME='$(SLIBNAME_WITH_VERSION)' 
SLIB_INSTALL_LINKS='$(SLIBNAME_WITH_MAJOR) $(SLIBNAME)'
将其修改成： 
SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'
LIB_INSTALL_EXTRA_CMD='$$(RANLIB) "$(LIBDIR)/$(LIBNAME)"'
SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'
SLIB_INSTALL_LINKS='$(SLIBNAME)'

然后新建一个build_android.sh文件。注意:要根据环境配置前四项，且每行末尾不能有空格

#!/bin/bash 
export TMPDIR="C:/Users/Jacket/Desktop/ff" 
NDK=C:/Users/Jacket/AppData/Local/Android/sdk/ndk-bundle 
SYSROOT=$NDK/platforms/android-21/arch-arm/ 
TOOLCHAIN=$NDK/toolchains/arm-linux-androideabi-4.9/prebuilt/windows-x86_64 
function build_one {
./configure \ 
--prefix=$PREFIX \ 
--enable-shared \ 
--disable-static \
--disable-doc \ 
--disable-ffmpeg \ 
--disable-ffplay \ 
--disable-ffprobe \ 
--disable-ffserver \ 
--disable-avdevice \ --disable-doc \ 
--disable-symver \
--cross-prefix=$TOOLCHAIN/bin/arm-linux-androideabi- \ 
--target-os=linux \
--arch=arm \
--enable-cross-compile \ 
--sysroot=$SYSROOT \ 
--extra-cflags="-Os -fpic $ADDI_CFLAGS" \ 
--extra-ldflags="$ADDI_LDFLAGS" \ 
$ADDITIONAL_CONFIGURE_FLAG
make clean
make
make install
}
CPU=arm
PREFIX=$(pwd)/android/$CPU
ADDI_CFLAGS="

启动MinGW进入FFmpeg源代码对应目录下执行命令脚本

chmod ./build_android.sh
./build_android.sh然后就开始编译了

下面开始移植到Android Studio中

1. 得到so库文件后，在libs目录下新建armeabi和include文件夹，将上面编译得到的android文件夹下对应的armeabi文件夹下的so库文件和include文件夹下的c头文件分别拷贝到libs下的armeabi和include文件夹下。如下图所示：
   

2. 编写CMakeLists.txt文件，在其中指明FFMpeg库文件目录

# 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)

# 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.
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 )

# 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(distribution_DIR ../../../../libs)

add_library( avcodec-57
SHARED
IMPORTED)
set_target_properties( avcodec-57
PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/armeabi/libavcodec-57.so)

add_library( avfilter-6
SHARED
IMPORTED)
set_target_properties( avfilter-6
PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/armeabi/libavfilter-6.so)

add_library( avformat-57
SHARED
IMPORTED)
set_target_properties( avformat-57
PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/armeabi/libavformat-57.so)

add_library( avutil-55
SHARED
IMPORTED)
set_target_properties( avutil-55
PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/armeabi/libavutil-55.so)

add_library( swresample-2
SHARED
IMPORTED)
set_target_properties( swresample-2
PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/armeabi/libswresample-2.so)

add_library( swscale-4
SHARED
IMPORTED)
set_target_properties( swscale-4
PROPERTIES IMPORTED_LOCATION
${distribution_DIR}/armeabi/libswscale-4.so)

include_directories(libs/include)


target_link_libraries( # Specifies the target library.
native-lib
avcodec-57
avfilter-6
avformat-57
avutil-55
swresample-2
swscale-4
# Links the target library to the log library
# included in the NDK.
${log-lib}
)

3.编写native方法，在C/C++文件中调用FFMpeg库提供的函数

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

extern "C" {
//编码
#include "libavcodec/avcodec.h"
//封装格式处理
#include "libavformat/avformat.h"
//像素处理
#include "libswscale/swscale.h"
//视频滤镜
#include "libavfilter/avfilter.h"
}

#define FFLOGI(FORMAT,...) __android_log_print(ANDROID_LOG_INFO,"ffmpeg",FORMAT,##__VA_ARGS__);
#define FFLOGE(FORMAT,...) __android_log_print(ANDROID_LOG_ERROR,"ffmpeg",FORMAT,##__VA_ARGS__);

extern "C"
JNIEXPORT jstring JNICALL
Java_com_jacket_ffmpeg_MainActivity_stringFromJNI(
JNIEnv *env,
jobject /* this */) {
// std::string hello = "Hello from C++";
// return env->NewStringUTF(hello.c_str());
// return env->NewStringUTF(av_version_info());
return env->NewStringUTF(avcodec_configuration());
}

extern "C"
JNIEXPORT void JNICALL
Java_com_jacket_ffmpeg_MainActivity_decode(JNIEnv *env, jclass type, jstring input_,
jstring output_) {
//获取输入输出文件名
const char *input = env->GetStringUTFChars(input_, 0);
const char *output = env->GetStringUTFChars(output_, 0);

//1.注册所有组件
av_register_all();

//封装格式上下文，统领全局的结构体，保存了视频文件封装格式的相关信息
AVFormatContext *pFormatCtx = avformat_alloc_context();

//2.打开输入视频文件
if (avformat_open_input(&pFormatCtx, input, NULL, NULL) != 0)
{
FFLOGE("%s","无法打开输入视频文件");
return;
}

//3.获取视频文件信息
if (avformat_find_stream_info(pFormatCtx,NULL) < 0)
{
FFLOGE("%s","无法获取视频文件信息");
return;
}

//获取视频流的索引位置
//遍历所有类型的流（音频流、视频流、字幕流），找到视频流
int v_stream_idx = -1;
int i = 0;
//number of streams
for (; i < pFormatCtx->nb_streams; i++)
{
//流的类型
if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
{
v_stream_idx = i;
break;
}
}

if (v_stream_idx == -1)
{
FFLOGE("%s","找不到视频流\n");
return;
}

//只有知道视频的编码方式，才能够根据编码方式去找到解码器
//获取视频流中的编解码上下文
AVCodecContext *pCodecCtx = pFormatCtx->streams[v_stream_idx]->codec;
//4.根据编解码上下文中的编码id查找对应的解码
AVCodec *pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
if (pCodec == NULL)
{
FFLOGE("%s","找不到解码器\n");
return;
}

//5.打开解码器
if (avcodec_open2(pCodecCtx,pCodec,NULL)<0)
{
FFLOGE("%s","解码器无法打开\n");
return;
}

//输出视频信息
FFLOGI("视频的文件格式：%s",pFormatCtx->iformat->name);
FFLOGI("视频时长：%d", (pFormatCtx->duration)/1000000);
FFLOGI("视频的宽高：%d,%d",pCodecCtx->width,pCodecCtx->height);
FFLOGI("解码器的名称：%s",pCodec->name);


//准备读取
//AVPacket用于存储一帧一帧的压缩数据（H264）
//缓冲区，开辟空间
AVPacket *packet = (AVPacket*)av_malloc(sizeof(AVPacket));

//AVFrame用于存储解码后的像素数据(YUV)
//内存分配
AVFrame *pFrame = av_frame_alloc();
//YUV420
AVFrame *pFrameYUV = av_frame_alloc();
//只有指定了AVFrame的像素格式、画面大小才能真正分配内存
//缓冲区分配内存
uint8_t *out_buffer = (uint8_t *)av_malloc(avpicture_get_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));
//初始化缓冲区
avpicture_fill((AVPicture *)pFrameYUV, out_buffer, AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);

//用于转码（缩放）的参数，转之前的宽高，转之后的宽高，格式等
struct SwsContext *sws_ctx = sws_getContext(pCodecCtx->width,pCodecCtx->height,pCodecCtx->pix_fmt,
pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P,
SWS_BICUBIC, NULL, NULL, NULL);
int got_picture, ret;

FILE *fp_yuv = fopen(output, "wb+");

int frame_count = 0;

//6.一帧一帧的读取压缩数据
while (av_read_frame(pFormatCtx, packet) >= 0)
{
//只要视频压缩数据（根据流的索引位置判断）
if (packet->stream_index == v_stream_idx)
{
//7.解码一帧视频压缩数据，得到视频像素数据
ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
if (ret < 0)
{
FFLOGE("%s","解码错误");
return;
}

//为0说明解码完成，非0正在解码
if (got_picture)
{
//AVFrame转为像素格式YUV420，宽高
//2 6输入、输出数据
//3 7输入、输出画面一行的数据的大小 AVFrame 转换是一行一行转换的
//4 输入数据第一列要转码的位置 从0开始
//5 输入画面的高度
sws_scale(sws_ctx, pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
pFrameYUV->data, pFrameYUV->linesize);

//输出到YUV文件
//AVFrame像素帧写入文件
//data解码后的图像像素数据（音频采样数据）
//Y 亮度 UV 色度（压缩了） 人对亮度更加敏感
//U V 个数是Y的1/4
int y_size = pCodecCtx->width * pCodecCtx->height;
fwrite(pFrameYUV->data[0], 1, y_size, fp_yuv);
fwrite(pFrameYUV->data[1], 1, y_size / 4, fp_yuv);
fwrite(pFrameYUV->data[2], 1, y_size / 4, fp_yuv);

frame_count++;
FFLOGI("解码第%d帧",frame_count);
}
}

//释放资源
av_free_packet(packet);
}

fclose(fp_yuv);

av_frame_free(&pFrame);

avcodec_close(pCodecCtx);

avformat_free_context(pFormatCtx);

env->ReleaseStringUTFChars(input_, input);
env->ReleaseStringUTFChars(output_, output);
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_jacket_ffmpeg_MainActivity_avfilterinfo(
JNIEnv * env,jobject){
char info[40000] = {0};
avfilter_register_all();

AVFilter *f_temp = (AVFilter *)avfilter_next(NULL);
while (f_temp != NULL){
sprintf(info,"%s%s\n",info,f_temp->name);
f_temp = f_temp->next;
}

return env->NewStringUTF(info);

}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_jacket_ffmpeg_MainActivity_avcodecinfo(
JNIEnv * env,jobject){
char info[40000] = {0};
av_register_all();

AVCodec *c_temp = av_codec_next(NULL);

while(c_temp != NULL){
if(c_temp->decode != NULL){
sprintf(info,"%sdecode:",info);
} else{
sprintf(info,"%sencode",info);
}
switch(c_temp->type){
case AVMEDIA_TYPE_VIDEO:
sprintf(info,"%s(video):",info);
break;
case AVMEDIA_TYPE_AUDIO:
sprintf(info,"%s(audio):",info);
break;
default:
sprintf(info,"%s(other):",info);
break;
}
sprintf(info,"%s[%10s]\n",info,c_temp->name);
c_temp = c_temp->next;
}
return env->NewStringUTF(info);
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_jacket_ffmpeg_MainActivity_avformatinfo(
JNIEnv * env,jobject){
char info[40000] = {0};
av_register_all();

AVInputFormat *if_temp = av_iformat_next(NULL);
AVOutputFormat *of_temp = av_oformat_next(NULL);
while (if_temp != NULL){
sprintf(info,"%sInput:%s\n",info,of_temp->name);
if_temp = if_temp->next;
}
while (of_temp != NULL){
sprintf(info,"%sOutput: %s\n",info,of_temp->name);
of_temp = of_temp->next;
}
return env->NewStringUTF(info);
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_jacket_ffmpeg_MainActivity_urlprotocolinfo(
JNIEnv * env,jobject){
char info[40000] = {0};
av_register_all();

struct URLProtocol *pup = NULL;
struct URLProtocol **p_temp = &pup;
avio_enum_protocols((void **)p_temp,0);

while ((*p_temp) != NULL){
sprintf(info,"%sInput: %s\n",info,avio_enum_protocols((void **)p_temp,0));
}
pup = NULL;
avio_enum_protocols((void **)p_temp,1);
while ((*p_temp) != NULL){
sprintf(info,"%sInput: %s\n",info,avio_enum_protocols((void **)p_temp,1));
}
return env->NewStringUTF(info);
}

可以看出，Java_com_jacket_ffmepg_MainActivity_stringFromJNI()根据宏定义判定了系统类型并且返回了一个字符串。在这里要注意，C语言中的Char[]是不能直接对应为Java中的String类型的(即jstring)。char[]转换为String需要通过JNIEnv的NewStringUTF()函数。为了调用FFMpeg而经过修改后的Java_com_jacket_ffmpeg_MainActivity_stringFromJN的源代码如下:

Java_com_jacket_ffmpeg_MainActivity_stringFromJNI(
        JNIEnv *env,
        jobject /* this */) {
  return env->NewStringUTF(avcodec_configuration());
}

在native-lib.cpp文件中调用libavcodec的avcodec_configuration()方法，用于获取FFMpeg的配置信息。该程序会输出FFMpeg类库下列信息

1. Protocol: FFMpeg类库支持的协议
2. AVFormat: FFMpeg类库支持的封装格式
3. AVCodec: FFMpeg类库支持的编解码器
4. AVFilter: FFMpeg类库支持的滤镜
5. Configure: FFMpeg类库的配置信息

最后在MainActivity中通过native方法调用C/C++函数

public class MainActivity extends AppCompatActivity implements View.OnClickListener
{

    // Used to load the 'native-lib' library on application startup.
    static
    {
        System.loadLibrary("native-lib");
//        System.loadLibrary("avcodec-57");
//        System.loadLibrary("avfilter-6");
//        System.loadLibrary("avformat-57");
//        System.loadLibrary("avutil-55");
//        System.loadLibrary("swresample-2");
//        System.loadLibrary("swscale-4");
    }

    private Button protocol,format,codec,filter;
    private TextView tv_info;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
    }


    private void init() {
        protocol = (Button) findViewById(R.id.btn_protocol);
        format = (Button) findViewById(R.id.btn_format);
        codec = (Button) findViewById(R.id.btn_codec);
        filter = (Button) findViewById(R.id.btn_filter);
        tv_info = (TextView) findViewById(R.id.tv_info);

        protocol.setOnClickListener(this);
        format.setOnClickListener(this);
        codec.setOnClickListener(this);
        filter.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btn_protocol:
                tv_info.setText(urlprotocolinfo());
                break;
            case R.id.btn_format:
                tv_info.setText(avformatinfo());
                break;
            case R.id.btn_codec:
                tv_info.setText(avcodecinfo());
                break;
            case R.id.btn_filter:
                tv_info.setText(avfilterinfo());
                break;
            default:
                break;
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item)
    {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings)
        {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    /**
     * A native method that is implemented by the 'native-lib' native library,
     * which is packaged with this application.
     */
    public native String stringFromJNI();

    public native void decode(String input, String output);

    public native String avfilterinfo();

    public native String avcodecinfo();

    public native String avformatinfo();

    public native String urlprotocolinfo();
}

运行结果如下所示:

最后附上本篇博客的代码:Github地址