Android LAME原生音频

前言

我想大家都做过录音的功能吧，首先想到的是不是MediaRecorder？今天我们不用MediaRecorder，而是使用LAME库自己编译音频编码模块，很明显，这个需要用到NDK。凡是涉及到音视频编解码这块的，都需要用到Android NDK(Native Development Kit)，原生开发工具包。即使用C/C++代码实现音频的采样和编码，然后使用Java去调用原生模块实现录音功能。

音视频相关基础知识

我来简单过一下基础的音视频相关知识。

Audio Sample：音频采样，通常指录制音频采样文件PCM的过程，PCM（脉冲编码调制）是一种音频流，称为裸流。人耳听到的是模拟信号，PCM是把声音从模拟信号转化为数字信号的技术。

Audio Track：音轨，封装格式的音频文件通常由多个音轨组成，比如MP3文件就是一种封装格式的音频文件，与之相对的就是音频原始采样数据PCM。比如一首歌，歌声是一个音轨，吉他声、鼓声等一些混合在其中的声音各自也是一个音轨。

Audio Channel：声道，比如左声道、右声道和环绕立体声。

Bitrate：比特率，俗称码率。它直接决定声音的清晰度即声音特征的详细程度，SQ、HQ音质是通过它来判断的，码率越高，音频文件越大，质量也越高。

Sample Rate：采样率，大多数沿用国际通用的标准采样率，即44.100kHZ或者48.000kHZ，肯定是不能录制超声波和次声波的，因为人耳感知不到。

录音和播放声音的详细过程。

录音：音频采样编码->音频封装

播放声音：音频解封装->音频解码播放

录音首先采样并编码得到PCM文件，然后封装PCM文件为MP3、WAV、FLAC等文件，播放声音首先也要解封装成PCM文件，然后对PCM文件解码播放。

编译共享库so

编译共享库so的过程有两种方式，一种是使用ndk-build+Android.mk+Application.mk，一种是CMake+CMakeLists.txt。今天我们采用最原始的方式，mk文件。其实Android.mk和CMakeLists.txt很多东西是一一对应的。

Android.mk	CMakeLists.txt
LOCAL_MODULE、LOCAL_SRC_FILES	add_library
LOCAL_CFLAGS	add_definitions
LOCAL_C_INCLUDES	include_directories
LOCAL_STATIC_LIBRARIES、LOCAL_SHARED_LIBRARIES	add_library + set_target_properties
LOCAL_LDLIBS	find_library

C文件

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Android.mk

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LAME_LIBMP3_DIR := lame-3.100_libmp3lameLOCAL_MODULE    := mp3lameLOCAL_SRC_FILES :=\
$(LAME_LIBMP3_DIR)/bitstream.c \
$(LAME_LIBMP3_DIR)/fft.c \
$(LAME_LIBMP3_DIR)/id3tag.c \
$(LAME_LIBMP3_DIR)/mpglib_interface.c \
$(LAME_LIBMP3_DIR)/presets.c \
$(LAME_LIBMP3_DIR)/quantize.c \
$(LAME_LIBMP3_DIR)/reservoir.c \
$(LAME_LIBMP3_DIR)/tables.c  \
$(LAME_LIBMP3_DIR)/util.c \
$(LAME_LIBMP3_DIR)/VbrTag.c \
$(LAME_LIBMP3_DIR)/encoder.c \
$(LAME_LIBMP3_DIR)/gain_analysis.c \
$(LAME_LIBMP3_DIR)/lame.c \
$(LAME_LIBMP3_DIR)/newmdct.c \
$(LAME_LIBMP3_DIR)/psymodel.c \
$(LAME_LIBMP3_DIR)/quantize_pvt.c \
$(LAME_LIBMP3_DIR)/set_get.c \
$(LAME_LIBMP3_DIR)/takehiro.c \
$(LAME_LIBMP3_DIR)/vbrquantize.c \
$(LAME_LIBMP3_DIR)/version.c \
MP3Encoder.cinclude $(BUILD_SHARED_LIBRARY)

LOCAL_PATH :=$(call my-dir)
当前文件在系统中的路径，必须为Android.mk文件的第一行。
include $(CLEAR_VARS)
清除上一次构建中的全局变量，开始一次新的编译。
LOCAL_MODULE
生成的模块的名称，这里是动态库so文件的名称，so文件的名称拼接为lib「模块名」.so
该模块的编译的目标名，用于区分各个模块，名字必须是唯一并不包含空格的，如果编译目标是 so 库，那么该 so 库的名称就是 lib 项目名 .so。
LOCAL_SRC_FILES
要编译的.c或.cpp文件，.h和.hpp文件可以不用出现在这里，系统会自动包含。
include $(BUILD_SHARED_LIBRARY)
include开头的是构建系统的内置变量，此行代码的意思是构建动态库，也称共享库，还有以下几种取值。
BUILD_STATIC_LIBRARY: 构建静态库。
PREBUILT_STATIC_LIBRARY: 将静态库包装成一个模块。
PREBUILT_SHARED_LIBRARY: 将静态库包装成一个模块。
BUILD_EXECUTABLE: 构建可执行文件。

Application.mk

APP_ABI := armeabi  armeabi-v7a  arm64-v8a  x86  x86_64  mips  mips64
APP_MODULES := mp3lame
APP_CFLAGS += -DSTDC_HEADERS
APP_PLATFORM := android-21

APP_ABI ABI（Application Binary Interface）应用二级制接口，这是一种计算机科学中的概念，用于描述软件库或操作系统与应用程序之间的二进制通信方式。它跟CPU指令集对应。
APP_MODULES 指定模块
APP_FLAGS 指定编译过程的flag，“DSTDC_HEADERS” 是一个编程中常见的宏定义，通常用于检查标准库头文件是否已经包含。这个宏定义通常在C/C++代码中使用，用于确保标准库的头文件已经正确包含，以便程序可以正常编译和运行。如果没有正确包含标准库头文件，编译器可能会报错或者出现未定义的行为。
APP_PLATFORM 指定创建的动态库的平台。

与JNI相关的文件

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>#ifndef _Included_Mp3Encoder
#define _Included_Mp3Encoder
#ifdef __cplusplus
extern "C" {
#endifJNIEXPORT void JNICALL Java_com_dorachat_dorachat_recorder_mp3_Mp3Encoder_init(JNIEnv *, jclass, jint, jint, jint, jint, jint);JNIEXPORT jint JNICALL Java_com_dorachat_dorachat_recorder_mp3_Mp3Encoder_encode(JNIEnv *, jclass, jshortArray, jshortArray, jint, jbyteArray);JNIEXPORT jint JNICALL Java_com_dorachat_dorachat_recorder_mp3_Mp3Encoder_flush(JNIEnv *, jclass, jbyteArray);JNIEXPORT void JNICALL Java_com_dorachat_dorachat_recorder_mp3_Mp3Encoder_close(JNIEnv *, jclass);#ifdef __cplusplus
}
#endif
#endif

lame的jni层主要定义4个方法init、encode、flush和close。

#include "lame-3.100_libmp3lame/lame.h"
#include "Mp3Encoder.h"static lame_global_flags *glf = NULL;JNIEXPORT void JNICALL Java_com_dorachat_dorachat_recorder_mp3_Mp3Encoder_init(JNIEnv *env, jclass cls, jint inSamplerate, jint outChannel,jint outSamplerate, jint outBitrate, jint quality) {if (glf != NULL) {lame_close(glf);glf = NULL;}glf = lame_init();lame_set_in_samplerate(glf, inSamplerate);lame_set_num_channels(glf, outChannel);lame_set_out_samplerate(glf, outSamplerate);lame_set_brate(glf, outBitrate);lame_set_quality(glf, quality);lame_init_params(glf);
}JNIEXPORT jint JNICALL
Java_com_dorachat_dorachat_recorder_mp3_Mp3Encoder_encode(JNIEnv *env, jclass cls, jshortArray buffer_l, jshortArray buffer_r,jint samples, jbyteArray mp3buf) {jshort* j_buffer_l = (*env)->GetShortArrayElements(env, buffer_l, NULL);jshort* j_buffer_r = (*env)->GetShortArrayElements(env, buffer_r, NULL);const jsize mp3buf_size = (*env)->GetArrayLength(env, mp3buf);jbyte* j_mp3buf = (*env)->GetByteArrayElements(env, mp3buf, NULL);int result = lame_encode_buffer(glf, j_buffer_l, j_buffer_r,samples, j_mp3buf, mp3buf_size);(*env)->ReleaseShortArrayElements(env, buffer_l, j_buffer_l, 0);(*env)->ReleaseShortArrayElements(env, buffer_r, j_buffer_r, 0);(*env)->ReleaseByteArrayElements(env, mp3buf, j_mp3buf, 0);return result;
}JNIEXPORT jint JNICALL
Java_com_dorachat_dorachat_recorder_mp3_Mp3Encoder_flush(JNIEnv *env, jclass cls, jbyteArray mp3buf) {const jsize mp3buf_size = (*env)->GetArrayLength(env, mp3buf);jbyte* j_mp3buf = (*env)->GetByteArrayElements(env, mp3buf, NULL);int result = lame_encode_flush(glf, j_mp3buf, mp3buf_size);(*env)->ReleaseByteArrayElements(env, mp3buf, j_mp3buf, 0);return result;
}JNIEXPORT void JNICALL Java_com_dorachat_dorachat_recorder_mp3_Mp3Encoder_close(JNIEnv *env, jclass cls) {lame_close(glf);glf = NULL;
}

这个需要你会一点C语言的基础，然后就可以轻松调用lame库的函数了。

package com.dorachat.dorachat.recorder.mp3;public class Mp3Encoder {static {System.loadLibrary("mp3lame");}public native static void close();public native static int encode(short[] buffer_l, short[] buffer_r, int samples, byte[] mp3buf);public native static int flush(byte[] mp3buf);public native static void init(int inSampleRate, int outChannel, int outSampleRate, int outBitrate, int quality);public static void init(int inSampleRate, int outChannel, int outSampleRate, int outBitrate) {init(inSampleRate, outChannel, outSampleRate, outBitrate, 7);}
}

我们再看一下java层。

Java层大致实现

我们录音肯定是要在后台Service中进行的，可以使用onStartCommand进行调用，这里只是一个简单的功能，就不使用aidl跨进程了。开始录音时我们需要开一个线程去采样音频数据。

public void start(String filePath, RecordConfig config) {this.currentConfig = config;if (state != RecordState.IDLE && state != RecordState.STOP) {Logger.e(TAG, "状态异常当前状态： %s", state.name());return;}resultFile = new File(filePath);String tempFilePath = getTempFilePath();LogUtils.dformat(TAG, "----------------开始录制 %s------------------------", currentConfig.getFormat().name());LogUtils.dformat(TAG, "参数： %s", currentConfig.toString());LogUtils.iformat(TAG, "pcm缓存 tmpFile: %s", tempFilePath);LogUtils.iformat(TAG, "录音文件 resultFile: %s", filePath);tmpFile = new File(tempFilePath);audioRecordThread = new AudioRecordThread();audioRecordThread.start();
}


private class AudioRecordThread extends Thread {private AudioRecord audioRecord;private int bufferSize;AudioRecordThread() {bufferSize = AudioRecord.getMinBufferSize(currentConfig.getSampleRate(),currentConfig.getChannelConfig(), currentConfig.getEncodingConfig()) * RECORD_AUDIO_BUFFER_TIMES;Logger.d(TAG, "record buffer size = %s", bufferSize);audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, currentConfig.getSampleRate(),currentConfig.getChannelConfig(), currentConfig.getEncodingConfig(), bufferSize);if (currentConfig.getFormat() == RecordConfig.RecordFormat.MP3) {if (mp3EncodeThread == null) {initMp3EncoderThread(bufferSize);} else {LogUtils.e("mp3EncodeThread != null, 请检查代码");}}}@Overridepublic void run() {super.run();switch (currentConfig.getFormat()) {case MP3:startMp3Recorder();break;default:startPcmRecorder();break;}}private void startPcmRecorder() {state = RecordState.RECORDING;notifyState();LogUtils.d("开始录制PCM");FileOutputStream fos = null;try {fos = new FileOutputStream(tmpFile);audioRecord.startRecording();byte[] byteBuffer = new byte[bufferSize];while (state == RecordState.RECORDING) {int end = audioRecord.read(byteBuffer, 0, byteBuffer.length);notifyData(byteBuffer);fos.write(byteBuffer, 0, end);fos.flush();}audioRecord.stop();files.add(tmpFile);if (state == RecordState.STOP) {makeFile();} else {LogUtils.i("暂停");}} catch (Exception e) {LogUtils.e(e.getMessage());notifyError("录音失败");} finally {try {if (fos != null) {fos.close();}} catch (IOException e) {e.printStackTrace();}}if (state != RecordState.PAUSE) {state = RecordState.IDLE;notifyState();LogUtils.d("录音结束");}}private void startMp3Recorder() {state = RecordState.RECORDING;notifyState();try {audioRecord.startRecording();short[] byteBuffer = new short[bufferSize];while (state == RecordState.RECORDING) {int end = audioRecord.read(byteBuffer, 0, byteBuffer.length);if (mp3EncodeThread != null) {mp3EncodeThread.addChangeBuffer(new Mp3EncodeThread.ChangeBuffer(byteBuffer, end));}notifyData(ByteUtils.toBytes(byteBuffer));}audioRecord.stop();} catch (Exception e) {LogUtils.e(e.getMessage());notifyError("录音失败");}if (state != RecordState.PAUSE) {state = RecordState.IDLE;notifyState();stopMp3Encoded();} else {LogUtils.d("暂停");}}
}private void stopMp3Encoded() {if (mp3EncodeThread != null) {mp3EncodeThread.stopSafe(new Mp3EncodeThread.EncordFinishListener() {@Overridepublic void onFinish() {notifyFinish();mp3EncodeThread = null;}});} else {LogUtils.e("mp3EncodeThread is null, 代码业务流程有误，请检查！");}
}private void makeFile() {switch (currentConfig.getFormat()) {case MP3:return;case WAV:mergePcmFile();makeWav();break;case PCM:mergePcmFile();break;default:break;}notifyFinish();LogUtils.i("录音完成！ path: %s ； 大小：%s", resultFile.getAbsoluteFile(), resultFile.length());
}/*** 添加Wav头文件。*/
private void makeWav() {if (!FileUtils.isFile(resultFile) || resultFile.length() == 0) {return;}byte[] header = WavUtils.generateWavFileHeader((int) resultFile.length(), currentConfig.getSampleRate(), currentConfig.getChannelCount(), currentConfig.getEncoding());WavUtils.writeHeader(resultFile, header);
}/*** 合并文件。*/
private void mergePcmFile() {boolean mergeSuccess = mergePcmFiles(resultFile, files);if (!mergeSuccess) {notifyError("合并失败");}
}/*** 合并PCM文件。** @param recordFile 输出文件* @param files      多个文件源* @return 是否成功*/
private boolean mergePcmFiles(File recordFile, List<File> files) {if (recordFile == null || files == null || files.size() <= 0) {return false;}FileOutputStream fos = null;BufferedOutputStream outputStream = null;byte[] buffer = new byte[1024];try {fos = new FileOutputStream(recordFile);outputStream = new BufferedOutputStream(fos);for (int i = 0; i < files.size(); i++) {BufferedInputStream inputStream = new BufferedInputStream(new FileInputStream(files.get(i)));int readCount;while ((readCount = inputStream.read(buffer)) > 0) {outputStream.write(buffer, 0, readCount);}inputStream.close();}} catch (Exception e) {LogUtils.e(e.getMessage());return false;} finally {try {if (outputStream != null) {outputStream.close();}if (fos != null) {fos.close();}} catch (IOException e) {e.printStackTrace();}}for (int i = 0; i < files.size(); i++) {files.get(i).delete();}files.clear();return true;
}/*** 根据当前的时间生成相应的文件名。*/
private String getTempFilePath() {String fileDir = String.format(Locale.getDefault(), "%s/Record/", Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC).getAbsolutePath());if (!FileUtils.createOrExistsDir(fileDir)) {LogUtils.e("文件夹创建失败：" + fileDir);}String fileName = String.format(Locale.getDefault(), "record_tmp_%s", FileUtils.getNowString(new SimpleDateFormat("yyyyMMdd_HH_mm_ss", Locale.SIMPLIFIED_CHINESE)));return String.format(Locale.getDefault(), "%s%s.pcm", fileDir, fileName);
}/*** 表示当前录制状态。*/
public enum RecordState {/*** 空闲状态。*/IDLE,/*** 录音中。*/RECORDING,/*** 暂停中。*/PAUSE,/*** 正在停止。*/STOP,/*** 录音流程结束（转换结束）。*/FINISH
}

在Mp3EncodeThread中init初始化录制参数，然后调用encode进行编码录制，录制完成调用flush把缓冲区冲一下水，清洗一下。最后调用一下close，完美。
最后附上录制流程细节的代码。

package com.dorachat.dorachat.recorder.mp3;import com.dorachat.dorachat.recorder.RecordConfig;
import com.dorachat.dorachat.recorder.RecordService;import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;public class Mp3EncodeThread extends Thread {private static final String TAG = Mp3EncodeThread.class.getSimpleName();private List<ChangeBuffer> cacheBufferList = Collections.synchronizedList(new LinkedList<ChangeBuffer>());private File file;private FileOutputStream os;private byte[] mp3Buffer;private EncodeFinishListener encodeFinishListener;/*** 是否已停止录音。*/private volatile boolean isOver = false;/*** 是否继续轮询数据队列。*/private volatile boolean start = true;public Mp3EncodeThread(File file, int bufferSize) {this.file = file;mp3Buffer = new byte[(int) (7200 + (bufferSize * 2 * 1.25))];RecordConfig currentConfig = RecordService.getCurrentConfig();int sampleRate = currentConfig.getSampleRate();Mp3Encoder.init(sampleRate, currentConfig.getChannelCount(), sampleRate, currentConfig.getRealEncoding());}@Overridepublic void run() {try {this.os = new FileOutputStream(file);} catch (FileNotFoundException e) {return;}while (start) {ChangeBuffer next = next();lameData(next);}}public void addChangeBuffer(ChangeBuffer changeBuffer) {if (changeBuffer != null) {cacheBufferList.add(changeBuffer);synchronized (this) {notify();}}}public void stopSafe(EncodeFinishListener encodeFinishListener) {this.encodeFinishListener = encodeFinishListener;isOver = true;synchronized (this) {notify();}}private ChangeBuffer next() {for (;;) {if (cacheBufferList == null || cacheBufferList.size() == 0) {try {if (isOver) {finish();}synchronized (this) {wait();}} catch (Exception e) {}} else {return cacheBufferList.remove(0);}}}private void lameData(ChangeBuffer changeBuffer) {if (changeBuffer == null) {return;}short[] buffer = changeBuffer.getData();int readSize = changeBuffer.getReadSize();if (readSize > 0) {int encodedSize = Mp3Encoder.encode(buffer, buffer, readSize, mp3Buffer);try {os.write(mp3Buffer, 0, encodedSize);} catch (IOException e) {}}}private void finish() {start = false;final int flushResult = Mp3Encoder.flush(mp3Buffer);if (flushResult > 0) {try {os.write(mp3Buffer, 0, flushResult);os.close();} catch (final IOException e) {}}if (encodeFinishListener != null) {encodeFinishListener.onFinish();}}public static class ChangeBuffer {private short[] rawData;private int readSize;public ChangeBuffer(short[] rawData, int readSize) {this.rawData = rawData.clone();this.readSize = readSize;}short[] getData() {return rawData;}int getReadSize() {return readSize;}}public interface EncodeFinishListener {/*** 格式转换完毕。*/void onFinish();}
}