Android编译Lame的全平台so库方案2，并实现转码mp3

迷南。 2022-06-08 11:38 286阅读 0赞

![20160901163927210][]

作者：谭东

时间：2017年9月24日

环境：Windows 7

Lame版本：Lame 3.99.5

LAME是目前最好的MP3编码引擎。LAME编码出来的MP3音色纯厚、空间宽广、低音清晰、细节表现良好，它独创的心理音响模型技术保证了CD音频还原的真实性，配合VBR和ABR参数，音质几乎可以媲美CD音频，但文件体积却非常小。对于一个免费引擎，LAME的优势不言而喻。

如果你需要将音频转码为mp3，就需要借助lame库。因为FFmpeg并不支持编码mp3。

因为ffmpeg自身也不支持转码Mp3，也是借助lame库实现的。

首先在官网[http://lame.sourceforge.net/][http_lame.sourceforge.net] 下载最新版的版本 lame-3.99.5 下载完进行解压，然后把libmp3lame目录下的文件拷贝到jni下面，去除i386文件夹，和非.c .h的文件，拷贝 lame.h （include目录下）到jni目录下。

编辑 jni/utils.h，把extern ieee754\_float32\_t fast\_log2(ieee754\_float32\_t x);替换为extern float fast\_log2(float x)。

ok，基本源码准备工作就做好了。

在Android上的编译如何新建项目等去我的前几篇文章看即可。

大致结构：

![20170924174605445][]

编写配置CMakeLists.txt

# 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.
    
    add_library( lame
                 SHARED
                 libs/include/liblame/bitstream.c
                 libs/include/liblame/encoder.c
                 libs/include/liblame/fft.c
                 libs/include/liblame/gain_analysis.c
                 libs/include/liblame/id3tag.c
                 libs/include/liblame/lame.c
                 libs/include/liblame/mpglib_interface.c
                 libs/include/liblame/newmdct.c
                 libs/include/liblame/presets.c
                 libs/include/liblame/psymodel.c
                 libs/include/liblame/quantize.c
                 libs/include/liblame/quantize_pvt.c
                 libs/include/liblame/reservoir.c
                 libs/include/liblame/set_get.c
                 libs/include/liblame/tables.c
                 libs/include/liblame/takehiro.c
                 libs/include/liblame/util.c
                 libs/include/liblame/vbrquantize.c
                 libs/include/liblame/VbrTag.c
                 libs/include/liblame/version.c
                 libs/include/liblame/xmm_quantize_sub.c)
    
    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 )
    set(distribution_DIR ${CMAKE_SOURCE_DIR}/../../../../libs)
    # 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
                           lame
                           # Links the target library to the log library
                           # included in the NDK.
                           ${log-lib} )

build.gradle里加入：

externalNativeBuild {
                cmake {
                    cFlags "-DSTDC_HEADERS"
                    cppFlags ""
                }
            }

是为了编译64位so库是防止出现 undefined symbol bcopy 这个错误的。  
在新建的jni的native-lib.cpp里编写测试获取lame版本的方法：

#include <jni.h>
    #include <string>
    #include "../../../libs/include/liblame/lame.h"
    
    extern "C" {
    
    JNIEXPORT jstring JNICALL
    Java_com_tandong_lame_MainActivity_stringFromJNI(
            JNIEnv *env,
            jobject /* this */) {
        std::string hello = "Hello from C++";
        return env->NewStringUTF(hello.c_str());
    }
    
    JNIEXPORT jstring JNICALL
    Java_com_tandong_lame_MainActivity_stringFromJNI2(
            JNIEnv *env,
            jobject /* this */) {
        return env->NewStringUTF(get_lame_version());
    }
    
    }

Activity里调用即可：

package com.tandong.lame;
    
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.widget.TextView;
    
    public class MainActivity extends AppCompatActivity {
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            // Example of a call to a native method
            TextView tv = (TextView) findViewById(R.id.sample_text);
            tv.setText(stringFromJNI2());
        }
    
        /**
         * A native method that is implemented by the 'native-lib' native library,
         * which is packaged with this application.
         */
        public native String stringFromJNI();
    
        public native String stringFromJNI2();
    
        // Used to load the 'native-lib' library on application startup.
        static {
            System.loadLibrary("native-lib");
        }
    }

后面就可以继续添加转码为mp3的音频格式的方法了。

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![20170830212011034][]

[20160901163927210]: /images/20220608/b5479d785f42448496ec0e67cc2fc810.png
[http_lame.sourceforge.net]: http://lame.sourceforge.net/
[20170924174605445]: /images/20220608/871b7f5f462044a8acd3c6c65a136c7d.png
[20170830212011034]: /images/20220608/622f9f9a99694b8795b4ae0c41a97cd3.png