AndroidStudio 2.2 开始支持 CMake 编译，网上的文章清一色都是 ndk-build，记录一下我用 CMake 搭建环境的过程。

基础环境

  • MacOS 10.12.3
  • AndroidStudio 2.3
  • NDK 13.1.*
  • FFmpeg 3.2.*

下载 FFmpeg 源码

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git clone https://git.ffmpeg.org/ffmpeg.git

切换到 3.2 分支

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git checkout -b 3.2 remotes/origin/release/3.2

当然你也可以去去官网下载压缩包。

编译 FFmpeg for Android

修改 FFmpeg 的 configure

打开 configure 文件，找到：

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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)'

替换成：

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SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'
LIB_INSTALL_EXTRA_CMD='$$(RANLIB)"$(LIBDIR)/$(LIBNAME)"'
SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'
SLIB_INSTALL_LINKS='$(SLIBNAME)'

编写 Android 编译脚本

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#!/bin/bash
NDK=/Users/gavin/Develop/android-sdk/ndk-bundle
SYSROOT=$NDK/platforms/android-15/arch-arm/
TOOLCHAIN=$NDK/toolchains/arm-linux-androideabi-4.9/prebuilt/darwin-x86_64

CPU=arm

PREFIX=$(pwd)/android/$CPU

ADDI_CFLAGS="-marm"

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
}

build_one

前三行自行更换成自己的 NDK 路径即可，PREFIX 就是最终编译输出地址，根据情况也可以修改。

保存文件到 FFmpeg 根目录为 build_android.sh， chmod +x build_android.sh 赋予执行权限。

编译

执行脚本进行编译。

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./build_android.sh

小憩一会儿，编译完成。

进入 PREFIX 目录：

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── include
│   ├── libavcodec
│   ├── libavfilter
│   ├── libavformat
│   ├── libavutil
│   ├── libswresample
│   └── libswscale
└── lib
    ├── libavcodec-57.so
    ├── libavfilter-6.so
    ├── libavformat-57.so
    ├── libavutil-55.so
    ├── libswresample-2.so
    ├── libswscale-4.so
    └── pkgconfig

我们需要的 so 和头文件都有啦。

导入 Android 工程

对于如何开始一个 C++ 项目，官方已经有中文文档了：

https://developer.android.google.cn/studio/projects/add-native-code.html

官网有的东西不赘述，再次声明学什么东西优先看 官方文档，官方文档，官方文档，并且 Google dev 现在已经有很多中文资源了。

新建一个 C/C++ 工程

勾选 Include C++ Support 即可得到一个基于 CMake 的模板工程。

拷贝 so 和 incude 文件到 libs

因为我们只编译了 arm 版本的 so，所以需要把 so 拷到 armeabi-v7a 目录下，完整路径如下：

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├── build.gradle
├── libs
│   ├── armeabi-v7a
│   │   ├── libavcodec-57.so
│   │   ├── libavfilter-6.so
│   │   ├── libavformat-57.so
│   │   ├── libavutil-55.so
│   │   ├── libswresample-2.so
│   │   └── libswscale-4.so
│   └── include
│       ├── libavcodec
│       ├── libavfilter
│       ├── libavformat
│       ├── libavutil
│       ├── libswresample
│       └── libswscale
├── proguard-rules.pro
└── src
    └── main
        ├── AndroidManifest.xml
        ├── cpp
        ├── java
        └── res

指定 jniLibs 路径

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android {
    ...
    sourceSets {
        main {
            jniLibs.srcDirs = ['libs']
        }
    }
}

指定 abiFilters

因为 so 只有 armeabi-v7a 的，所以我们还需要指定一下 abi 为 armeabi-v7a

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android {
    ...
    defaultConfig {
      ...
      ndk {
          abiFilters 'armeabi-v7a'
      }
    }
}

编写 CMakeLists

脚本怎么写，有什么讲究其实官方文档已经很清楚了：
创建 CMake 构建脚本

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# 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 )

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( avformat-57
             SHARED
             IMPORTED )
set_target_properties( avformat-57
                       PROPERTIES IMPORTED_LOCATION
                       ../../../../libs/armeabi-v7a/libavformat-57.so )

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( swscale-4
             SHARED
             IMPORTED )
set_target_properties( swscale-4
                       PROPERTIES IMPORTED_LOCATION
                       ../../../../libs/armeabi-v7a/libswscale-4.so )


include_directories( libs/include )

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.
                       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} )

Java 引入 so 库

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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");
}

运行测试一下

如果成功运行不报错的话，就证明一切没有问题。

编写 FFmpeg 测试代码

UI

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="cn.gavinliu.android.ffmpeg.MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="protocol"
            android:text="Protocol"
            android:textAllCaps="false" />

        <Button
            android:id="@+id/button2"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="filter"
            android:text="Filter"
            android:textAllCaps="false" />

        <Button
            android:id="@+id/button3"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="format"
            android:text="Format"
            android:textAllCaps="false" />

        <Button
            android:id="@+id/button4"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="codec"
            android:text="Codec"
            android:textAllCaps="false" />
    </LinearLayout>

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:id="@+id/sample_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:scrollbars="vertical"
            android:text="Hello World!" />
    </ScrollView>
</LinearLayout>
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package cn.gavinliu.android.ffmpeg;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    // 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 TextView tv;

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

        // Example of a call to a native method
        tv = (TextView) findViewById(R.id.sample_text);
        tv.setText(stringFromJNI());
    }

    public void protocol(View view) {
        tv.setText(urlprotocolinfo());
    }

    public void filter(View view) {
        tv.setText(avformatinfo());
    }

    public void format(View view) {
        tv.setText(avfilterinfo());
    }

    public void codec(View view) {
        tv.setText(avcodecinfo());
    }


    /**
     * 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 avformatinfo();

    public native String urlprotocolinfo();

    public native String avcodecinfo();

    public native String avfilterinfo();
}

C++

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#include <jni.h>
#include <string>

extern "C" {

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavfilter/avfilter.h>

JNIEXPORT jstring JNICALL
Java_cn_gavinliu_android_ffmpeg_MainActivity_stringFromJNI(
        JNIEnv *env,
        jobject /* this */) {

    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

JNIEXPORT jstring JNICALL
Java_cn_gavinliu_android_ffmpeg_MainActivity_avformatinfo(
        JNIEnv *env,
        jobject /* this */) {
    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);
}

JNIEXPORT jstring JNICALL
Java_cn_gavinliu_android_ffmpeg_MainActivity_urlprotocolinfo(
        JNIEnv *env,
        jobject /* this */) {

    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);
}

JNIEXPORT jstring JNICALL
Java_cn_gavinliu_android_ffmpeg_MainActivity_avcodecinfo(
        JNIEnv *env,
        jobject /* this */) {

    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);
}

JNIEXPORT jstring JNICALL
Java_cn_gavinliu_android_ffmpeg_MainActivity_avfilterinfo(JNIEnv *env, jobject /* this */) {

    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);
}
}

运行

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