作者：譚東

時間：2017年9月24日

環境：Windows 7

Lame版本：Lame 3.99.5

LAME是目前最好的MP3編碼引擎。LAME編碼出來的MP3音色純厚、空間寬廣、低音清晰、細節表現良好，它獨創的心理音響模型技術保證了CD音頻還原的真實性，配合VBR和ABR參數，音質幾乎可以媲美CD音頻，但文件體積卻非常小。對于一個免費引擎，LAME的優勢不言而喻。

如果你需要將音頻轉碼為mp3，就需要借助lame庫。因為FFmpeg并不支持編碼mp3。

因為ffmpeg自身也不支持轉碼Mp3，也是借助lame庫實現的。

首先在官網http://lame.sourceforge.net/?下載最新版的版本 lame-3.99.5 下載完進行解壓，然后把libmp3lame目錄下的文件拷貝到jni下面，去除i386文件夾，和非.c .h的文件，拷貝 lame.h (include目錄下)到jni目錄下。

編輯 jni/utils.h，把extern ieee754_float32_t fast_log2(ieee754_float32_t x);替換為extern float fast_log2(float x)。

ok，基本源碼準備工作就做好了。

在Android上的編譯如何新建項目等去我的前幾篇文章看即可。

大致結構：

編寫配置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 ""

}

}是為了編譯64位so庫是防止出現

undefined symbol bcopy 這個錯誤的。

在新建的jni的native-lib.cpp里編寫測試獲取lame版本的方法：

#include

#include

#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里調用即可：

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");

}

}

后面就可以繼續添加轉碼為mp3的音頻格式的方法了。

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總結

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