一、交叉编译LAME库
LAME是一种非常优秀的MP3编码引擎，在业界，转码成MP3格式的音频文件时，最常用的编码器就是LAME库。
1. 下载LAME库源码
https://sourceforge.net/projects/lame/files/lame/
进入LAME官网下载LAME源码，我选择最新版本：3.100
2. 配置交叉编译环境
在编译LAME之前，我们需要先配置交叉编译环境。
Android NDK附带了交叉工具链，具体参考这篇文章：https://developer.android.com/ndk/guides/other_build_systems?hl=zh-cn
我的NDK路径为：/home/lorien/Android/Sdk/ndk/22.1.7171670/toolchains/llvm/prebuilt/linux-x86_64/bin
3. 配置、编译、安装LAME
首先我们需要编译使用的一些环境变量：
#!/bin/bash
export TOOLCHAIN=/home/lorien/Android/Sdk/ndk/22.1.7171670/toolchains/llvm/prebuilt/linux-x86_64
export TARGET=aarch64-linux-android
export API=21
export AR=$TOOLCHAIN/bin/llvm-ar
export CC=$TOOLCHAIN/bin/$TARGET$API-clang
export AS=$CC
export CXX=$TOOLCHAIN/bin/$TARGET$API-clang++
export LD=$TOOLCHAIN/bin/ld
export RANLIB=$TOOLCHAIN/bin/llvm-ranlib
export STRIP=$TOOLCHAIN/bin/llvm-strip
export CFLAGS="-fPIC"
接下来解压的LAME源码：lame-3.100.tar.gz，解压后进入源码根目录：/lame-3.100
配置：
./configure --host=arm-linux --disable-shared --disable-frontend --enable-static --prefix=/Users/zhanghao43/Desktop/lame/arm64-v8a
编译：
make clean
make -j4
安装：
make install
安装完成后，生成的头文件和库文件，就会在prefix指定的路径下面，即：/Users/zhanghao43/Desktop/lame/arm64-v8a
在生成的文件中，接下来需要使用的文件是：
- 头文件：/Users/zhanghao43/Desktop/lame/arm64-v8a/include/lame/lame.h
- 库文件：/Users/zhanghao43/Desktop/lame/arm64-v8a/lib/lame/libmp3lame.a
至此，LAME库交叉编译完成。
二、创建Android Native项目使用LAME库
下面我们使用LAME库创建一个Android Demo项目，完成PCM音频的录制以及PCM文件转MP3的功能
我们需要创建Android Natvie项目。
1. 配置工程
我们先把编译LAME库生成的头文件和库文件放到项目中，路径如下图：
然后，我们修改下CMakeLists.txt，让CMake在编译、链接时，找到LAME头文件和库文件。CMakeLists.txt文件内容如下：
cmake_minimum_required(VERSION 3.10.2)
# Declares and names the project.
project("lame")
include_directories(
${CMAKE_SOURCE_DIR}/include/lame)
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 mp3_encoder.cpp)
add_library(mp3lame STATIC IMPORTED)
set_target_properties(mp3lame PROPERTIES IMPORTED_LOCATION
${CMAKE_SOURCE_DIR}/../jniLibs/${ANDROID_ABI}/libmp3lame.a)
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 )
target_link_libraries(native-lib
mp3lame)
2. C++代码
接下来，可以写代码了。首先看一下mp3_encoder.h, mp3_encoder.cpp
#ifndef LAME_MP3ENCODER_H
#define LAME_MP3ENCODER_H
#include <stdio.h>
#include "lame.h"
class Mp3Encoder {
private:
FILE* pcmFile;
FILE* mp3File;
lame_t lameClient;
public:
Mp3Encoder();
~Mp3Encoder();
int Init(const char* pcmFilePath, const char* mp3FilePath, int sampleRate, int channels, int bitRate);
void Encode();
void Destroy();
};
#endif //LAME_MP3ENCODER_H
#include "mp3_encoder.h"
#include "lame.h"
Mp3Encoder::Mp3Encoder() {
}
int Mp3Encoder::Init(const char* pcmFilePath, const char* mp3FilePath, int sampleRate, int channels, int bitRate) {
int ret = -1;
pcmFile = fopen(pcmFilePath, "rb");
if (pcmFile) {
mp3File = fopen(mp3FilePath, "wb");
if (mp3File) {
lameClient = lame_init();
// in 采样率
lame_set_in_samplerate(lameClient, sampleRate);
// out 采样率
lame_set_out_samplerate(lameClient, sampleRate);
lame_set_num_channels(lameClient, channels);
lame_set_brate(lameClient, bitRate / 1000);
lame_init_params(lameClient);
ret = 0;
}
}
return ret;
}
void Mp3Encoder::Encode() {
int bufferSize = 1024 * 256;
short *buffer = new short[bufferSize / 2];
short *leftBuffer = new short[bufferSize / 4];
short *rightBuffer = new short[bufferSize / 4];
unsigned char* mp3_buffer = new unsigned char[bufferSize];
size_t readBufferSize = 0;
while ((readBufferSize = fread(buffer, 2, bufferSize / 2, pcmFile)) > 0) {
for (int i = 0; i < readBufferSize; i++) {
if (i % 2 == 0) {
leftBuffer[i / 2] = buffer[i];
} else {
rightBuffer[i / 2] = buffer[i];
}
}
size_t wroteSize = lame_encode_buffer(lameClient, (short int *) leftBuffer, (short int *) rightBuffer, (int)(readBufferSize / 2), mp3_buffer, bufferSize);
fwrite(mp3_buffer, 1, wroteSize, mp3File);
}
delete [] buffer;
delete [] leftBuffer;
delete [] rightBuffer;
delete [] mp3_buffer;
}
void Mp3Encoder::Destroy() {
if (pcmFile) {
fclose(pcmFile);
}
if (mp3File) {
fclose(mp3File);
lame_close(lameClient);
}
}
然后我们看一下native-lib.cpp中的JNI方法：
Mp3Encoder *encoder;
extern "C" JNIEXPORT jint JNICALL
Java_com_baidu_lame_MainActivity_pcmToMp3JNI(
JNIEnv *env,
jobject,
jstring pcm_path,
jstring mp3_path,
jint sample_rate,
jint channel,
jint bit_rate) {
const char *pcmPath = env->GetStringUTFChars(pcm_path, NULL);
const char *mp3Path = env->GetStringUTFChars(mp3_path, NULL);
encoder = new Mp3Encoder();
encoder->Init(pcmPath, mp3Path, sample_rate, channel, bit_rate);
encoder->Encode();
env->ReleaseStringUTFChars(pcm_path, pcmPath);
env->ReleaseStringUTFChars(mp3_path, mp3Path);
return 0;
}
3. Java代码
先贴一下MainAcgtivity的XML文件
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="开始录制pcm"
android:onClick="startRecordPcm"
/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="停止录制pcm"
android:onClick="stopRecordPcm"
/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="pcm转mp3"
android:onClick="pcm2mp3"
/>
</LinearLayout>
MainActivity.kt
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
external fun stringFromJNI(): String
external fun pcmToMp3JNI(pcmPath: String, mp3Path: String,
sampleRate: Int, channel: Int, bitRate: Int): Int
companion object {
init {
System.loadLibrary("native-lib")
}
}
private lateinit var audioRecord: AudioRecord
private var pcmFilePath: String = ""
private var buffersize = 1024
private var isRecord = false
/**
* 调用Native代码完成PCM文件转成MP3
*/
fun pcm2mp3(view: View) {
val pcmPath = getPCMFile().absolutePath
val mp3Path = getMP3File().absolutePath
val sampleRate = 44100
val channel = 2
val bitRate = 64000
val ret = pcmToMp3JNI(pcmPath, mp3Path, sampleRate, channel, bitRate)
Toast.makeText(this, "$ret", Toast.LENGTH_SHORT).show()
}
/**
* 开始录制PCM音频文件
*/
@SuppressLint("MissingPermission")
fun startRecordPcm(view: View) {
val frequency = 44100
val channelConfig = AudioFormat.CHANNEL_IN_STEREO
val audioEncoding = AudioFormat.ENCODING_PCM_16BIT
buffersize = AudioRecord.getMinBufferSize(frequency, channelConfig, audioEncoding)
audioRecord = AudioRecord(
MediaRecorder.AudioSource.MIC,
frequency,
channelConfig,
audioEncoding,
buffersize)
pcmFilePath = getPCMFile().absolutePath
isRecord = true
RecordThread().start()
}
/**
* 结束录制PCM音频文件
*/
fun stopRecordPcm(view: View) {
isRecord = false
}
private fun getPCMFile(): File {
val root = getExternalFilesDir(null)
val csvDir = File(root, "/audio/")
if (!csvDir.exists()) {
// 创建csv 目录
csvDir.mkdir()
}
return File(csvDir, "sing.pcm")
}
private fun getMP3File(): File {
val root = getExternalFilesDir(null)
val csvDir = File(root, "/audio/")
if (!csvDir.exists()) {
// 创建csv 目录
csvDir.mkdir()
}
return File(csvDir, "sing.mp3")
}
/**
* 录制PCM音频线程
*/
inner class RecordThread : Thread() {
override fun run() {
audioRecord.startRecording()
var fos: FileOutputStream? = null
try {
Log.d(TAG, "pcm文件：$pcmFilePath")
fos = FileOutputStream(pcmFilePath)
val bytes = ByteArray(buffersize)
while (isRecord) {
audioRecord.read(bytes, 0, bytes.size)
fos.write(bytes, 0, bytes.size)
fos.flush()
}
Log.d(TAG, "停止录制")
audioRecord.stop()
fos.flush()
} catch (e: Exception) {
Log.d(TAG, "exception: $e")
} finally {
if (fos != null) {
try {
fos.close()
} catch (e: Exception) {
}
}
}
}
}
}
最后，权限：
<!--录音-->
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<!--读取SD卡-->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
代码中，没有动态申请权限，APP装上后，需要再到设置页面给APP开下对应权限才能录制音频。
OK，本文到这就结束了，感谢大家阅读。