[Cmake-Android音视频]创建支持ffmpeg3.4的项目

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/adolph_lu/article/details/90477243

AndroidStudio版本3.2

1.创建Android项目

1.1打开AndroidStudio,创建一个名为FirstFfmpeg的项目，勾选C++支持

1.2 minimun SDK选择5.0，4.0或者4.1都可以，根据自身项目需求

1.3 C++ Standard 选择C++11

1.4等待Android项目创建完成

为了方便查看Android文件目录，可以将Android视图结构切换为Project

2.导入已经编译好的ffmpeg头文件和库文件

2.1导入ffmpeg库头文件：复制编译好的ffmpeg的动态库中的头文件到app目录下

2.2导入ffmpeg动态库文件：在app/libs下新建armeabi-v7a文件夹，将动态库复制到该目录下

3.编写CMakeLists.txt文件，Android会默认生成这个文件，我们只需要修改即可，如下，添加的地方都有详细的注释，相信都能看得懂

# 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.

#添加头文件目录，相对于CMakeLists.txt也就是本文件的路径，从目录
#结构中可以看出，CMakeLists.txt和include目录是在同一级目录
include_directories(include)

#设置ffmpeg库所在路径的变量 FF为表示路径的变量，
#CMAKE_CURRENT_SOURCE_DIR为CMake内置变量，表示CMakeLists所在的目录
#ANDROID_ABI CPU架构类型，如果gradle文件没有设置过滤，
#则会表示所有的架构，arm-v7a arm-v8a x86 x86_64
#所以FF=CMAKE_CURRENT_SOURCE_DIR/libs/armeabi-v7a
set(FF ${CMAKE_CURRENT_SOURCE_DIR}/libs/${ANDROID_ABI})

#添加avcodec SHARED表示动态库 IMPORTED表示从外部导入
add_library(avcodec SHARED IMPORTED)
set_target_properties(avcodec PROPERTIES IMPORTED_LOCATION ${FF}/libavcodec.so)

#avformat
add_library(avformat SHARED IMPORTED)
set_target_properties(avformat PROPERTIES IMPORTED_LOCATION ${FF}/libavformat.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)

# 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.

#将添加进来的库avcodec avformat链接到native-lib库中，
#因为我们最终只会生成一个libnative-lib.so库
#这个库如果没有指定路径，那么可以在app/build/cmake/debug/obj中找到
target_link_libraries( # Specifies the target library.
        native-lib
        avcodec avformat
        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

4在native-lib.cpp中添加avcodec.h头文件，调用avcodec_configuration()打印ffmpeg configure参数

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

//ffmpeg是基于C语言的库，所以在使用ffmpeg的头文件的时候，需要用extern来标记
extern "C"
{
#include <libavcodec/avcodec.h>
}

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

5.修改app下build.gradle,主要是设置只编译armeabi-v7a架构，设置ffmpeg动态库目录

    defaultConfig {
        applicationId "c.lucas.firstffmpeg"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++11"
            }
            //只编译armeabi-v7a架构
            ndk {
                abiFilters "armeabi-v7a"
            }
        }
        //设置ffmpeg动态库目录 相对于app下的build.gradle文件目录
        sourceSets{
            main{
                jniLibs.srcDirs=['libs']
            }
        }
    }

6.最后编译运行，可以在手机屏幕上看到ffmpeg的编译配置信息。