主要的流程

1.新建好android studio工程
2.在main下新建一个jni的目录，并且把编译好的ffmpeg复制到路径下
3.编写java文件，编写native方法，生成头文件，复制到当前路径下。
4.编写cpp文件，include相关的头文件
5.选择编译工程，生成so。
6.在java文件中loadlibrary。加载so库

遇到的问题

编译的ffmpeg是32位和64位时

        externalNativeBuild {
            cmake {
                cppFlags " -std=c++11"
                abiFilters  'armeabi'//需要保持一致
            }
        }
    }
//使用编译好的so的路径
    packagingOptions {
        exclude 'META-INF/LICENSE'
        pickFirst 'lib/armeabi/libFFmpeg4Android-lib.so'
    }
//如果遇到错误，此处需要添加一下
    sourceSets.main {
    //    jniLibs.srcDir 'src/main/libs'
        jni.srcDirs = [] //disable automatic ndk-build call
    }

问题：导入ffmpeg头文件编译时，遇到编译报错

//解：.Putting includes within extern "C" block may work.
extern "C"{
#include "ffmpeg.h"
#include "include/libavformat/avformat.h"
}

问题：CMakeList.txt文件的编写,导入的头文件路径，编译的时候会报错头文件找不到，根据当前文件的目录结构，需要手动修改头文件中路径。

# 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)
#C 的编译选项是 CMAKE_C_FLAGS
# 指定编译参数，可选
if(${ANDROID_ABI} STREQUAL "armeabi-v7a")
    include_directories(${ANDROID_SYSROOT}/usr/include/arm-linux-androideabi)
elseif(${ANDROID_ABI} STREQUAL "arm64-v8a")
    include_directories(${ANDROID_SYSROOT}/usr/include/aarch64-linux-android)
else()
    include_directories(${ANDROID_SYSROOT}/usr/include/arm-linux-androideabi)
endif()
SET(CMAKE_CXX_FLAGS "-Wno-error=format-security -Wno-error=pointer-sign")

#设置生成的so动态库最后输出的路径
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../jniLibs/${ANDROID_ABI})
set(distribution_DIR ${PROJECT_SOURCE_DIR})
# 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.
             FFmpeg4Android-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             FFmpeg4Android-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 )
add_library( avcodec-57
             SHARED
             IMPORTED)
set_target_properties( avcodec-57
                       PROPERTIES IMPORTED_LOCATION
                       ${distribution_DIR}/libavcodec-57.so)
add_library( avdevice-57
             SHARED
             IMPORTED)
set_target_properties( avdevice-57
                       PROPERTIES IMPORTED_LOCATION
                       ${distribution_DIR}/libavdevice-57.so)
add_library( avfilter-6
             SHARED
             IMPORTED)
set_target_properties( avfilter-6
                       PROPERTIES IMPORTED_LOCATION
                       ${distribution_DIR}/libavfilter-6.so)

add_library( avformat-57
             SHARED
             IMPORTED)
set_target_properties( avformat-57
                       PROPERTIES IMPORTED_LOCATION
                       ${distribution_DIR}/libavformat-57.so)

add_library( avutil-55
             SHARED
             IMPORTED)
set_target_properties( avutil-55
                       PROPERTIES IMPORTED_LOCATION
                       ${distribution_DIR}/libavutil-55.so)

add_library( swresample-2
             SHARED
             IMPORTED)
set_target_properties( swresample-2
                       PROPERTIES IMPORTED_LOCATION
                       ${distribution_DIR}/libswresample-2.so)

add_library( swscale-4
             SHARED
             IMPORTED)
set_target_properties( swscale-4
                       PROPERTIES IMPORTED_LOCATION
                       ${distribution_DIR}/libswscale-4.so)
include_directories(src/main/jni/)
# 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.
                       FFmpeg4Android-lib
                       avcodec-57
                       avdevice-57
                       avfilter-6
                       avformat-57
                       avutil-55
                       swresample-2
                       swscale-4
                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )