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9. 创建支持ffmpeg的AndroidStudio项目并调用其接口在界面显示库配置信息~1

发布时间：2021-05-28 14:51:30编辑：雪饮阅读（）

 建立安卓項目

建立一個ndk的安卓項目以安卓4.1爲例

以上篇中編譯出來的neon方式的這個ffmpeg輸出爲例。
處理頭文件
\root\ff\ffmpeg-3.4\android\armv7-a-neon-hard\include目錄到剛才新建的這個安卓項目的app目錄下
然後新安卓項目的cpp/native-lib.cpp中引入待會兒要用的c的頭文件：
#include <jni.h>
#include <string>
extern "C"{
    #include <libavcodec/avcodec.h>
}
extern "C" JNIEXPORT jstring JNICALL
Java_com_example_ndk_1and_141_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}
注意：extern "C" 表示引入的是C語言的頭文件而不是c++的，因爲ffmpeg是c語言寫的
既然上面cpp/native-cpp使用了頭文件，那麽cpp/CMakeLists.txt要定義頭文件路徑應該從什麽地方加載

# 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("ndk_and_41")

# 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.
#添加頭文件路徑(括號中的include是相對於本文件路徑)
include_directories(../../../include)
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 )

# 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.

target_link_libraries( # Specifies the target library.
                       native-lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

原來cpp/native-lib.cpp中剛才包含c頭文件的地方可能是紅色警告狀態，此時在build=>refresh linked C++ projects操作執行后就會自動鏈接成功，不會報紅色警告態了。

并且此時ctrl+鼠標左鍵就可以打開這個頭文件了。
此時將項目編譯安裝到目標AVD安卓4.1中，這裏遇到了一點問題，一直沒有什麽明顯的響應。此時我嘗試單獨啓動這個目標AVD也是一直卡在shuttingdown
經過網上資料處理方法為刪除這個目標AVD然後重新創建目標AVD，這個問題可能是上次沒有正常關閉目標AVD所導致。
這個問題修復好了之後，重新回到主題重新編譯運行項目到目標AVD是沒有問題的。
處理so庫文件
拷貝\root\ff\ffmpeg-3.4\android\armv7-a-neon-hard\lib中所有.so後綴的文件到上面新建這個安卓項目的app\libs下創建的armeabi-v7a目錄中
然後在cpp/CMakeLists.txt中添加要用的so庫並鏈接這個要用的so庫
# 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("ndk_and_41")

# 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.
#添加頭文件路徑(括號中的include是相對於本文件路徑)
include_directories(../../../include)
#設置ffmpeg庫所在路徑的變量，這裏的FF是自定義的一個名字
set(FF ${CMAKE_CURRENT_SOURCE_DIR}../../../libs/${ANDROID_ABI})
#avcodec這個是自定義的一個名字
add_library(avcodec SHARED IMPORTED)
set_target_properties(avcodec PROPERTIES IMPORTED_LOCATION ${FF}/libavcodec.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).
             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.

target_link_libraries( # Specifies the target library.
                       native-lib
                       avcodec
                       #這裏將avcodec庫鏈接進來
                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

abi過濾處理

接著在app/build.gradle中配置：
plugins {
    id 'com.android.application'
}

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.example.ndk_and_41"
        minSdkVersion 16
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++11"
            }
            ndk{
                abiFilters "armeabi-v7a"
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.10.2"
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

因爲這裏只處理armeabi-v7a種類的abi，其它的暫時不考慮，只編譯這一個版本的abi。

另外這個文件中也要設置庫路徑：
plugins {
    id 'com.android.application'
}

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.example.ndk_and_41"
        minSdkVersion 16
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++11"
            }
            ndk{
                abiFilters "armeabi-v7a"
            }
        }
        sourceSets{
            main{
                jniLibs.srcDirs=['libs']
            }
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.10.2"
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

這裏的libs也是本安卓項目中的庫路徑的libs文件夾

輸出ffmpeg的編譯配置相關信息
回到cpp/native-lib.cpp中用avcodec_configuration函數輸出ffmpeg的編譯配置相關信息
如果能輸出成功，那麽本篇的實驗就成功了。

#include <jni.h>
 #include <string>
 
 extern "C"{
     #include <libavcodec/avcodec.h>
 }
 extern "C" JNIEXPORT jstring JNICALL
 Java_com_example_ndk_1and_141_MainActivity_stringFromJNI(
         JNIEnv* env,
         jobject /* this */) {
     std::string hello = "Hello from C++";
     hello+=avcodec_configuration();
     return env->NewStringUTF(hello.c_str());
 }

理論上到這一步就完事了，但是實際最終編譯的時候可能會在build output中輸出如下錯誤信息：

More than one file was found with OS independent path 'lib/armeabi-v7a/libavcodec.so'. If you are using jniLibs and CMake IMPORTED targets, see https://developer.android.com/studio/preview/features#automatic_packaging_of_prebuilt_dependencies_used_by_cmake

這裏的意思是說和lib/armeabi-v7a/libavcodec.so這個庫重複了，不知道怎麽選擇了。

那麽這裏的處理方法是重複了讓其選擇第一個。

app/build.gradle:

plugins {
     id 'com.android.application'
 }
 
 android {
     compileSdkVersion 30
     buildToolsVersion "30.0.3"
 
     defaultConfig {
         applicationId "com.example.ndk_and_41"
         minSdkVersion 16
         targetSdkVersion 30
         versionCode 1
         versionName "1.0"
 
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
         externalNativeBuild {
             cmake {
                 cppFlags "-std=c++11"
             }
             ndk{
                 abiFilters "armeabi-v7a"
             }
         }
         sourceSets{
             main{
                 jniLibs.srcDirs=['libs']
             }
         }
     }
     packagingOptions {
         pickFirst 'lib/armeabi-v7a/libavcodec.so'
     }
 
     buildTypes {
         release {
             minifyEnabled false
             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
         }
     }
     externalNativeBuild {
         cmake {
             path "src/main/cpp/CMakeLists.txt"
             version "3.10.2"
         }
     }
     compileOptions {
         sourceCompatibility JavaVersion.VERSION_1_8
         targetCompatibility JavaVersion.VERSION_1_8
     }
 }
 
 dependencies {
 
     implementation 'androidx.appcompat:appcompat:1.2.0'
     implementation 'com.google.android.material:material:1.3.0'
     implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
     testImplementation 'junit:junit:4.+'
     androidTestImplementation 'androidx.test.ext:junit:1.1.2'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
 }

接下來分別測試了安卓4.1、4.2、4.3（API 18）以及真機測試魅族16t，就最好兩個可以用。前面幾個不可以用，報錯：

could not load needed library 'libavcodec.so' for 'libnative-lib.so'  至于这个问题应该没有对应的动态链接库。

這個錯誤在有些android studio中不會出現，只會直接崩潰，比如我的臺式機，而在我筆記本上這個錯誤是報錯了的。

下面這個就是在真機魅族16t上面成功編譯出來的。