Android开发学习之路--Android Studio cmake编译ffmpeg

  最新的android studio2.2引入了cmake可以很好地实现ndk的编写。这里使用最新的方式，对于以前的android下的ndk编译什么的可以参考之前的文章:Android开发学习之路–NDK、JNI之初体验。

1.ffmpeg编译

  进入正题，既然是ffmpeg的移植编译，那么就先下载ffmpeg，https://ffmpeg.org/download.html#releases。这里下载的是3.0.3版本。
  新建ffmpeg文件夹，然后新建脚本用来编译ffmpeg，命名为build.sh，脚本如下：

#!/bin/bashcd ffmpegexport TMPDIR=/Users/jared/Desktop/jared/study/external/ffmpeg/tempdirNDK=/Users/jared/Desktop/jared/software/sdk/ndk-bundleSYSROOT=$NDK/platforms/android-16/arch-arm/TOOLCHAIN=/Users/jared/Desktop/jared/software/sdk/ndk-bundle/toolchains/arm-linux-androideabi-4.9/prebuilt/darwin-x86_64CPU=armPREFIX=/Users/jared/Desktop/jared/study/external/ffmpeg/outputADDI_CFLAGS="-marm"function build_one{    ./configure \        --prefix=$PREFIX \        --enable-shared \        --disable-static \        --disable-doc \        --disable-ffmpeg \        --disable-ffplay \        --disable-ffprobe \        --disable-ffserver \        --disable-doc \        --disable-symver \        --enable-small \        --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}build_onecd ../

  注意的是这里的路径是对应的ndk的相关路径。

  然后chmod 777 build.sh，然后执行source build.sh。开始编译ffmpeg。小憩片刻之后，编译完成，在output目录下就会生成对应的so文件:

➜  ffmpeg cd output➜  output lsinclude lib➜  output cd lib➜  lib lslibavcodec-57.so   libavfilter-6.so   libavutil-55.so    libswscale-4.solibavcodec.so      libavfilter.so     libavutil.so       libswscale.solibavdevice-57.so  libavformat-57.so  libswresample-2.so pkgconfiglibavdevice.so     libavformat.so     libswresample.so➜  lib

  编译完成，这里只是用了arm的平台，如果需要mips，或者x86需要修改build.sh脚本的arch和路径这里不赘述了。
  既然库文件都已经编译出来了那就可以android开搞了。

2.android环境搭建

  首先需要最新的android studio2.2，并且安装好cmake和ndk。然后新建工程，可以开始了。
  新建工程取名为helloffmpeg，然后选中include c++ support，然后下一步直到新建完成为止。如下图：

  然后比一般的工程多了些东西，首先是build.gradle了，

  CMake的cpp的flags

externalNativeBuild {            cmake {                cppFlags ""            }        }

  CMake的路径

externalNativeBuild {        cmake {            path "CMakeLists.txt"        }    }

  然后看CMakeLists.txt文件，这里主要讲解下配置。先看下已经配置好的库文件：

# 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 )set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../libs)add_library( avutil-55             SHARED             IMPORTED )set_target_properties( avutil-55                       PROPERTIES IMPORTED_LOCATION                       ../../../../libs/armeabi-v7a/libavutil-55.so )add_library( swresample-2             SHARED             IMPORTED )set_target_properties( swresample-2                       PROPERTIES IMPORTED_LOCATION                       ../../../../libs/armeabi-v7a/libswresample-2.so )add_library( avcodec-57             SHARED             IMPORTED )set_target_properties( avcodec-57                       PROPERTIES IMPORTED_LOCATION                       ../../../../libs/armeabi-v7a/libavcodec-57.so )add_library( avfilter-6             SHARED             IMPORTED)set_target_properties( avfilter-6                       PROPERTIES IMPORTED_LOCATION                       ../../../../libs/armeabi-v7a/libavfilter-6.so )add_library( swscale-4             SHARED             IMPORTED)set_target_properties( swscale-4                       PROPERTIES IMPORTED_LOCATION                       ../../../../libs/armeabi-v7a/libswscale-4.so )add_library( avdevice-57             SHARED             IMPORTED)set_target_properties( avdevice-57                       PROPERTIES IMPORTED_LOCATION                       ../../../../libs/armeabi-v7a/libavdevice-57.so )add_library( avformat-57             SHARED             IMPORTED)set_target_properties( avformat-57                       PROPERTIES IMPORTED_LOCATION                       ../../../../libs/armeabi-v7a/libavformat-57.so )set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")add_library( native-lib             SHARED             src/main/cpp/native-lib.cpp )include_directories(libs/include)#target_include_directories(native-lib PRIVATE libs/include)target_link_libraries( native-lib swresample-2 avcodec-57 avfilter-6 swscale-4 avdevice-57 avformat-57                       ${log-lib} )

  cmake_minimum_required(VERSION 3.4.1):表示cmake的最低版本是3.4.1。
  add_library():添加库，分为两种，一种是需要编译为库的代码，一种是已经编译好的库文件。
  比如上面编译好的ffmpeg的库，

add_library( avutil-55             SHARED             IMPORTED )

  这里avutil-55表示库的名称，SHARED表示是共享库，一般.so文件，还有STATIC，一般.a文件。IMPORTED表示引用的不是生成的。
  接着是这里用到的需要生产的.so文件

add_library( native-lib             SHARED             src/main/cpp/native-lib.cpp )

  最后的参数是源码的路径，如果有更多的源码就接下去写上。

  set_target_properties：对于已经编译好的so文件需要引入，所以需要设置。

set_target_properties( avutil-55                       PROPERTIES IMPORTED_LOCATION                       ../../../../libs/armeabi-v7a/libavutil-55.so )

  这里avutil-55是名字，然后是PROPERTIES IMPORTED_LOCATION加上库的路径。
  include_directories：一般外面引入的库文件需要头文件，所以可以通过这个来引入：

include_directories(libs/include)

  target_link_libraries：链接，把需要的so文件链接起来，这里native-lib需要链接ffmpeg的库文件。

  最后看下和java，res同级的cpp目录下有native-lib.cpp文件，系统自动生成的。
  首先是native-lib.cpp内容：

#include <jni.h>#include <string>extern "C"jstringJava_com_jared_helloffmpeg_MainActivity_stringFromJNI(        JNIEnv *env, jobject) {    std::string hello = "Hello from C++";    return env->NewStringUTF(hello.c_str());}

  这里有一个函数Java_com_jared_helloffmpeg_MainActivity_stringFromJNI，命名方式也可以知道，Java开头，com_jared_helloffmpeg为包名，MainActivity是调用的java类，最后stringFromJNI是方法名。然后返回了hello from c++字符。

  看下java的代码：

 // Example of a call to a native method TextView tv = (TextView) findViewById(R.id.sample_text); tv.setText(avformatinfo());/**  * A native method that is implemented by the 'native-lib' native library,  * which is packaged with this application. */  public native String stringFromJNI();  // Used to load the 'native-lib' library on application startup.    static {        loadLibrary("native-lib");    }

  也很好理解这里的stringFromJNI的native方法，具体需要看jni的基本概念了，这里就不多赘述了。好了基本上最简单的通了，那么接下去就是ffmpeg的使用了。

3.修改使用ffmpeg

  接着来修改界面显示ffmpeg的一些基本信息。如下：

<?xml version="1.0" encoding="utf-8"?><layout>    <data class="MainBinding"></data>    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"        xmlns:tools="http://schemas.android.com/tools"        android:id="@+id/activity_main"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:orientation="vertical"        android:paddingBottom="@dimen/activity_vertical_margin"        android:paddingLeft="@dimen/activity_horizontal_margin"        android:paddingRight="@dimen/activity_horizontal_margin"        android:paddingTop="@dimen/activity_vertical_margin"        tools:context="com.jared.helloffmpeg.MainActivity">        <LinearLayout            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:orientation="horizontal">            <Button                android:id="@+id/btn_protocol"                android:layout_width="wrap_content"                android:layout_height="wrap_content"                android:layout_margin="2dp"                android:text="Protocol"                android:textAllCaps="false" />            <Button                android:id="@+id/btn_format"                android:layout_width="wrap_content"                android:layout_height="wrap_content"                android:layout_margin="2dp"                android:text="Format"                android:textAllCaps="false" />            <Button                android:id="@+id/btn_codec"                android:layout_width="wrap_content"                android:layout_height="wrap_content"                android:layout_margin="2dp"                android:text="Codec"                android:textAllCaps="false" />            <Button                android:id="@+id/btn_filter"                android:layout_width="wrap_content"                android:layout_height="wrap_content"                android:layout_margin="2dp"                android:text="Filter"                android:textAllCaps="false" />        </LinearLayout>        <ScrollView            android:layout_width="match_parent"            android:layout_height="wrap_content">            <TextView                android:id="@+id/tv_info"                android:layout_width="match_parent"                android:layout_height="wrap_content"                android:text="Hello World!" />        </ScrollView>    </LinearLayout></layout>

  主要是实现了四个button，分别是protocol，format，codec和filter。如下图所示：

  
  修改jni部分的代码，也就是native-lib.cpp的代码如下：

#include <jni.h>#include <string>extern "C"{#include <libavcodec/avcodec.h>#include <libavformat/avformat.h>#include <libavfilter/avfilter.h>jstringJava_com_jared_helloffmpeg_MainActivity_stringFromJNI(        JNIEnv *env, jobject) {    std::string hello = "Hello from C++";    return env->NewStringUTF(hello.c_str());}jstringJava_com_jared_helloffmpeg_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);}jstringJava_com_jared_helloffmpeg_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, if_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);}jstringJava_com_jared_helloffmpeg_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);}jstringJava_com_jared_helloffmpeg_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);}}

  这里要特别注意ffmpeg的头文件已经调用的代码要extern “C”里面，要不然会报错误的。

  最后就是java调用代码了。如下所示：

package com.jared.helloffmpeg;import android.databinding.DataBindingUtil;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.view.View;import com.jared.helloffmpeg.databinding.MainBinding;import static java.lang.System.loadLibrary;public class MainActivity extends AppCompatActivity implements View.OnClickListener {    private MainBinding binding;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        //setContentView(R.layout.activity_main);        binding = DataBindingUtil.setContentView(this, R.layout.activity_main);        binding.btnProtocol.setOnClickListener(this);        binding.btnCodec.setOnClickListener(this);        binding.btnFilter.setOnClickListener(this);        binding.btnFormat.setOnClickListener(this);        // Example of a call to a native method        //TextView tv = (TextView) findViewById(R.id.sample_text);        //tv.setText(avformatinfo());    }    @Override    public void onClick(View view) {        switch (view.getId()) {            case R.id.btn_protocol:                binding.tvInfo.setText(urlprotocolinfo());                break;            case R.id.btn_format:                binding.tvInfo.setText(avformatinfo());                break;            case R.id.btn_codec:                binding.tvInfo.setText(avcodecinfo());                break;            case R.id.btn_filter:                binding.tvInfo.setText(avfilterinfo());                break;            default:                break;        }    }    /**     * A native method that is implemented by the 'native-lib' native library,     * which is packaged with this application.     */    public native String stringFromJNI();    public native String urlprotocolinfo();    public native String avformatinfo();    public native String avcodecinfo();    public native String avfilterinfo();    // Used to load the 'native-lib' library on application startup.    static {        loadLibrary("native-lib");    }}

  都准备好了，那么就继续运行看看结果了：

  基本上Android Studio下的cmake编译ffmpeg就到此结束了，那么接下去就可以在android手机上使用ffmpeg来做一些音视频相关的东西了。

github源码下载地址