ffmpeg.so在Android中的使用

• 如果你还没有FFmpeg.so文件，前请往获取：FFmpeg编译Android端so文件纪要(附资源下载)

前言： 在这个过程中请尽量克制你的小心思，按照步骤走通后再展现你的骚操作。

1、AndroidStudio创建C++工程

2、拷贝include文件夹（跟ffmpeg一起生成的）以及ffmpeg.so文件到工程中

3、打开CMakeLists文件，加入ffmpeg，如下：

• ${CMAKE_SOURCE_DIR} 标识CMakeLists所在目录地址

# 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.
#创建和命名一个库，将其设置为静态的
#或共享，并提供到其源代码的相对路径。
#您可以定义多个库，然后CMake为您构建它们。
#Gradle自动将共享库打包到你的APK中。

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)

####### 这里是新加的 #######
add_library( ffmpeg
        SHARED
        IMPORTED)
set_target_properties( ffmpeg
        PROPERTIES IMPORTED_LOCATION
        ${CMAKE_SOURCE_DIR}/libs/arm64-v8a/libffmpeg.so)

#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.
#搜索指定的预构建库并将路径存储为
#变量。因为CMake在搜索路径中包含了系统库
#默认情况下，您只需要指定公共NDK库的名称
#要添加。CMake验证以前是否存在该库
#完成它的构建。

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.
#指定CMake应该链接到目标库的库。你
#可以链接多个库，比如您在本文中定义的库吗
#构建脚本、预构建的第三方库或系统库。

####### 这里是新加的 #######
include_directories(src/main/cpp/include/)

target_link_libraries( # Specifies the target library.
        native-lib
        ffmpeg
        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

4、修改完成后先build一下工程，保证到这一步没有错误，如果出错可以按以下方法排查

• 检查地址引用的地址是否正确
• 从最后开始一段一段注释掉代码，通过构建检查是否有错误
  

5、再确保以构建没有问题之后进入native-lib.cpp，修改如下：

• so库中的头文件必须使用 extern “C” 包起来引用，千万不要使用Alt+Enter导入，否则会报错，错误为：
  [1/2] Building CXX object CMakeFiles/native-lib.dir/src/main/cpp/native-lib.cpp.o
  [2/2] Linking CXX shared library …\build\intermediates\cmake\debug\obj\arm64-v8a\libnative-lib.so

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

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

/*********************************** 以下是新加的 ***********************************/

// so库中的头文件必须使用 extern "C" 包起来引用，否则会报错
extern "C" {
#include "include/libavcodec/avcodec.h"
}

extern "C"
JNIEXPORT jstring JNICALL
Java_com_包名_包名_MainActivity_stringTest(JNIEnv *env,
                                                         jobject /* this */) {
  char info[10000] = {0};
  // 这里随便找了个文件打印部分内容，用来验证可以正常使用FFmpeg了
  sprintf(info, "%s\n", avcodec_configuration());
  return env->NewStringUTF(info);
}

同时在MainActivity中使用：

public class MainActivity extends AppCompatActivity {

  // Used to load the 'native-lib' library on application startup.
  static {
    System.loadLibrary("native-lib");
  }

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

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

  /**
   * 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 stringTest();  // 这个就是在native_lib.cpp 中新加的方法
}

6、最后别忘了在app.build中加入：

    defaultConfig {
        applicationId "com.xxx.xxx"
        ***
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++11"
            }
        }
        ndk {
            abiFilters "arm64-v8a"
        }
    }

    // 必须有，否则so文件可能不会被打包进APK
    sourceSets {
        main {
            jniLibs.srcDirs = ['libs']
        }
    }

7、好了，跑起来看看效果吧！