在Android中使用FFmpeg进阶2

通过上一篇文章我们已经学习了如果通过源码编译出FFmpeg的动态库文件，这篇文章我们学习下如何将so文件集成到Android工程中。这篇文章主要包含以下几个内容：

• 如何将FFMPEG 能力集成到native C++工程
• 如何在一个现有的android 工程中添加JNI接口

• 在Android中使用FFmpeg进阶1
• 在Android中使用FFmpeg进阶3

编译构建

新建一个native C++工程

在Android Studio中新建一个native C++工程。

集成FFmpeg

将ffmpeg编译好的文件放到libs文件夹下，如下图，以armeabi-v7a为例。

如下面所示，将CmakeLists做一个简单配置。

# 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 3.10.2)

# Declares and names the project.

project("ffmpegdemo")
set(CURRENT_DIR ${CMAKE_SOURCE_DIR})
message("CURRENT_DIR: " ${CMAKE_SOURCE_DIR})
set(LIBS_DIR D:/developProject/hangliebe/FFmpegDemo/app/libs)
# include_directories(${LIBS_DIR}/armeabi-v7a/include)

include_directories(${LIBS_DIR}/arm64-v8a/include/arm64-v8a)

# 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).
             native-lib.cpp
             FFmpegTest.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.


add_library(avcodec
        SHARED
        IMPORTED)
set_target_properties(avcodec
        PROPERTIES IMPORTED_LOCATION
        ${LIBS_DIR}/arm64-v8a/lib/arm64-v8a/libavcodec.so)

add_library(avdevice
        SHARED
        IMPORTED)
set_target_properties(avdevice
        PROPERTIES IMPORTED_LOCATION
        ${LIBS_DIR}/arm64-v8a/lib/arm64-v8a/libavdevice.so)

add_library(avformat
        SHARED
        IMPORTED)
set_target_properties(avformat
        PROPERTIES IMPORTED_LOCATION
        ${LIBS_DIR}/arm64-v8a/lib/arm64-v8a/libavformat.so)

add_library(avutil
        SHARED
        IMPORTED)
set_target_properties(avutil
        PROPERTIES IMPORTED_LOCATION
        ${LIBS_DIR}/arm64-v8a/lib/arm64-v8a/libavutil.so)

add_library(swresample
        SHARED
        IMPORTED)
set_target_properties(swresample
        PROPERTIES IMPORTED_LOCATION
        ${LIBS_DIR}/arm64-v8a/lib/arm64-v8a/libswresample.so)

add_library(swscale
        SHARED
        IMPORTED)
set_target_properties(swscale
        PROPERTIES IMPORTED_LOCATION
        ${LIBS_DIR}/arm64-v8a/lib/arm64-v8a/libswscale.so)

add_library(avfilter
        SHARED
        IMPORTED)
set_target_properties(avfilter
        PROPERTIES IMPORTED_LOCATION
        ${LIBS_DIR}/arm64-v8a/lib/arm64-v8a/libavfilter.so)


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
        avfilter
        avformat
        avcodec
        avdevice
        avutil
        swresample
        swscale
        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

build_gradle中添加NDK配置

android {
    ……
    defaultConfig {
        ……
        ndk {
            // 这里添加的对应cpu类型的.so库。下面以为例，初次外，可继续添加其他ABI等类型
            abiFilters 'armeabi-v7a' /*, 'x86', 'x86_64' */ 
        }
    }
    ……
}

然后执行Sync构建，可以看到构建成功。

使用FFmpeg

FFmpegTest.cpp

//
// Created by Administrator on 2021/11/21.
//

#include "FFmpegTest.h"

extern "C" {
#include <libavformat/avformat.h>
}

unsigned FFmpegTest::getAvFormatVersion() {
    return avformat_version();
}

MainActivity中将native代码返回值显示出来。

@Override
protected void onCreate(Bundle savedInstanceState) {
    ……
    // Example of a call to a native method
    TextView tv = binding.sampleText;
    tv.setText("avFormat version:" + getAvFormtVersion());
}
// 该函数在native中实现会进一步调用FFmpegTest::getAvFormatVersion
public native int getAvFormtVersion(); 

效果

在现有的Android工程中添加JNI

添加cpp目录

在app/src/main中添加cpp目录，用于存放native源码文件。

添加CMakeLists文件

在app目录中添加CMakeLists文件，用于构建项目。

设置build.gradle

指定CMakeLists文件路径

android {
    ……
    externalNativeBuild {
        cmake {
            path file('CMakeLists.txt')
            version '3.10.2'
        }
    }
    ……
}

创建源码，编译的so在java中使用

在cpp中添加源码文件，并且对应修改CMakeLists文件，并将编译的结果在java代码中加载。以下是案例中的几个重要修改点：

java文件

static {
System.loadLibrary("native-lib");
}
    
public native String stringFromJNI();

c++文件

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

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

CmakeLists.txt

cmake_minimum_required(VERSION 3.10.2)

project("native-lib")

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)


find_library( # Sets the name of the path variable.
              log-lib

              log )

编译通过后，就可以在java中通过JNI接口访问native代码

接下来，就可以在工程中集成FFmpeg能力。