1）把编译生成的so库复制到libs文件夹下，同时把include里面的头文件也复制到libs文件夹下。

2）在build.gradle中添加一下代码

defaultConfig {
        applicationId "com.houde.ffmpeg.test"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
                abiFilters 'armeabi-v7a'
            }
        }
        sourceSets{
            main{
                jniLibs.srcDirs = ['libs']
            }
        }
        ndk{
            abiFilters 'armeabi-v7a'
        }
    }

3)在CMakeList.txt中添加一下代码

include_directories(libs/include)
set(DIR ${CMAKE_SOURCE_DIR}/libs)
add_library(avcodec
        SHARED
        IMPORTED)
set_target_properties(avcodec
        PROPERTIES IMPORTED_LOCATION
        ${DIR}/armeabi-v7a/libavcodec.so)

add_library(avdevice
        SHARED
        IMPORTED)
set_target_properties(avdevice
        PROPERTIES IMPORTED_LOCATION
        ${DIR}/armeabi-v7a/libavdevice.so)
add_library(avformat
        SHARED
        IMPORTED)
set_target_properties(avformat
        PROPERTIES IMPORTED_LOCATION
        ${DIR}/armeabi-v7a/libavformat.so)
add_library(avutil
        SHARED
        IMPORTED)
set_target_properties(avutil
        PROPERTIES IMPORTED_LOCATION
        ${DIR}/armeabi-v7a/libavutil.so)
add_library(postproc
        SHARED
        IMPORTED)
set_target_properties(postproc
        PROPERTIES IMPORTED_LOCATION
        ${DIR}/armeabi-v7a/libpostproc.so)
add_library(swresample
        SHARED
        IMPORTED)
set_target_properties(swresample
        PROPERTIES IMPORTED_LOCATION
        ${DIR}/armeabi-v7a/libswresample.so)
add_library(swscale
        SHARED
        IMPORTED)
set_target_properties(swscale
        PROPERTIES IMPORTED_LOCATION
        ${DIR}/armeabi-v7a/libswscale.so)
add_library(avfilter
        SHARED
        IMPORTED)
set_target_properties(avfilter
        PROPERTIES IMPORTED_LOCATION
        ${DIR}/armeabi-v7a/libavfilter.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)
target_link_libraries( # Specifies the target library.
        native-lib
        avfilter
        avcodec
        avdevice
        avformat
        avutil
        postproc
        swresample
        swscale
        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

4)检查配置的so是否正确,在native-lib.cpp文件中引入libavcodec/avcodec.h，修改返回的字符串内容：

 std::string hello = avcodec_configuration();
    return env->NewStringUTF(hello.c_str());

显示结果：

错误记录：
1）ffmpeg函数不能被识别
编译是出现" undefined reference to 'avcodec_register_all()"和“Error:(15) undefined reference to 'avcodec_configuration()”，错误如下

Error:(15) undefined reference to 'avcodec_register_all()'
Error:(15) undefined reference to 'avcodec_configuration()'

这是因为ffmpeg是一个纯C语言编写的库，使用C++调用C代码时候，需要使用“extern “C””包围头文件“avcodec.h”和相关代码，如下：

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

#ifdef __cplusplus
extern "C" {
#endif

#include "libavcodec/avcodec.h"
#include "libavutil/avutil.h"

JNIEXPORT jstring JNICALL
Java_com_houde_ffmpeg_test_MainActivity_stringFromJNI(
        JNIEnv *env,
        jobject /* this */) {
    std::string hello = avcodec_configuration();
    return env->NewStringUTF(hello.c_str());
}
#ifdef __cplusplus
};
#endif

参考文章：
https://www.jianshu.com/p/435bb46b33a9
https://blog.csdn.net/eieihihi/article/details/74153201