上篇文章我们介绍了音频输出(音乐播放)，本文将介绍音频的录音即输入，文章中代码坏境Android 4.4

音频输入类：

MediaRecorder

AudioRecord

首先录制音频需要在 AndroidManifest.xml 中加入权限

1、MediaRecorder

MediaRecorder是Android 提供媒体文件录制的类，可以录制视频和音频，我们这主要的是录制音频，下面先看一段录音的代码：

package com.example.framework;

import java.io.File;

import android.app.Activity;

import android.media.MediaRecorder;

import android.media.MediaRecorder.AudioEncoder;

import android.media.MediaRecorder.AudioSource;

import android.media.MediaRecorder.OutputFormat;

import android.os.Bundle;

public class MediaRecorderActivity extends Activity {

private MediaRecorder mRediaRecorder;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

try {

String path = new File(getCacheDir(), "audio.mp4").getAbsolutePath();

mRediaRecorder = new MediaRecorder();

mRediaRecorder.setAudioChannels(2);

mRediaRecorder.setAudioSource(AudioSource.MIC);

mRediaRecorder.setAudioSamplingRate(44100);

mRediaRecorder.setOutputFormat(OutputFormat.MPEG_4);

mRediaRecorder.setOutputFile(path);

mRediaRecorder.setAudioEncoder(AudioEncoder.DEFAULT);

mRediaRecorder.prepare();

mRediaRecorder.start();

} catch (Exception e) {

e.printStackTrace();

}

}

@Override

protected void onDestroy() {

super.onDestroy();

if (mRediaRecorder != null) {

mRediaRecorder.stop();

mRediaRecorder.release();

}

}

}

参数说明：

AudioChannels

声道，Android中取值范围：1或者2，1代表单声道，2代表双声道(立体声)

AudioSource

音频源，Android中已经定义好常量，android.media.MediaRecorder.AudioSource 类

public final class AudioSource {

private AudioSource() {}

/** Default audio source **/

public static final int DEFAULT = 0;

/** Microphone audio source */

public static final int MIC = 1;

/** Voice call uplink (Tx) audio source */

public static final int VOICE_UPLINK = 2;

/** Voice call downlink (Rx) audio source */

public static final int VOICE_DOWNLINK = 3;

/** Voice call uplink + downlink audio source */

public static final int VOICE_CALL = 4;

/** Microphone audio source with same orientation as camera if available, the main

* device microphone otherwise */

public static final int CAMCORDER = 5;

public static final int VOICE_RECOGNITION = 6;

public static final int VOICE_COMMUNICATION = 7;

public static final int REMOTE_SUBMIX = 8;

}AudioSource.DEFAULT 默认

AudioSource.MIC  麦克风

AudioSource.VOICE_UPLINK  电话上行

AudioSource.VOICE_DOWNLINK 电话下行

AudioSource.VOICE_CALL 电话 上行+下行

AudioSource.CAMCORDER 摄像机

AudioSource.VOICE_RECOGNITION 语音识别

AudioSource.VOICE_COMMUNICATION 语音通信，例如VoIP

AudioSource.REMOTE_SUBMIX 远程声音，例如wifi display

电话录音：AudioSource.VOICE_UPLINK，AudioSource.VOICE_DOWNLINK，AudioSource.VOICE_CALL 需要系统权限

AudioSource.REMOTE_SUBMIX 需要在AndroidManifest中加入

SamplingRate

采样率，一般取值范围在8000-48000，取值越大声音越好，采样率高文件也会更大

OutputFormat

输出格式，Android中已经定义好常量，android.media.MediaRecorder.OutputFormat 类

public final class OutputFormat {

private OutputFormat() {}

public static final int DEFAULT = 0;

/** 3GPP media file format*/

public static final int THREE_GPP = 1;

/** MPEG4 media file format*/

public static final int MPEG_4 = 2;

/** The following formats are audio only .aac or .amr formats */

/**

* AMR NB file format

* @deprecated Deprecated in favor of MediaRecorder.OutputFormat.AMR_NB

*/

public static final int RAW_AMR = 3;

/** AMR NB file format */

public static final int AMR_NB = 3;

/** AMR WB file format */

public static final int AMR_WB = 4;

/** @hide AAC ADIF file format */

public static final int AAC_ADIF = 5;

/** AAC ADTS file format */

public static final int AAC_ADTS = 6;

/** @hide Stream over a socket, limited to a single stream */

public static final int OUTPUT_FORMAT_RTP_AVP = 7;

/** @hide H.264/AAC data encapsulated in MPEG2/TS */

public static final int OUTPUT_FORMAT_MPEG2TS = 8;

}介绍几种常用的格式, @hide 隐藏的，开发中避免使用，新的版本中就可能去掉该格式的支持。

OutputFormat.THREE_GPP

3gp格式

OutputFormat.MPEG_4

mp4格式

OutputFormat.AMR_NB

OutputFormat.AMR_WB

AMR_NB和AMR_WB的算法不一样.

OutputFormat.AAC_ADTS

ADTS 全称是(Audio Data Transport Stream) 主要用于音频流传输.

文件格式中并没有看到MP3,Android暂时不支持MP3格式，可以自己录制PCM数据编码成MP3 ，后面我们会介绍PCM数据的录制

OutputFile

录音的文件保存路径

AudioEncoder

音频编码，编码定义常量类，android.media.MediaRecorder.AudioEncoder

public final class AudioEncoder {

/* Do not change these values without updating their counterparts

* in include/media/mediarecorder.h!

*/

private AudioEncoder() {}

public static final int DEFAULT = 0;

/** AMR (Narrowband) audio codec */

public static final int AMR_NB = 1;

/** AMR (Wideband) audio codec */

public static final int AMR_WB = 2;

/** AAC Low Complexity (AAC-LC) audio codec */

public static final int AAC = 3;

/** High Efficiency AAC (HE-AAC) audio codec */

public static final int HE_AAC = 4;

/** Enhanced Low Delay AAC (AAC-ELD) audio codec */

public static final int AAC_ELD = 5;

}对于不同的文件格式选择不同的编码

录制MP4或者AAC_ADTS格式时选用编码 AudioEncoder.AAC,AudioEncoder.HE_AAC,AudioEncoder.AAC_ELD

录制3gp或者amr格式时选用编码 AudioEncoder.AMR_NB,AudioEncoder.AMR_WB

MediaRecorder录音的主要步骤

1：设置参数

2：prepare 准备

3：start 开始录音

4：stop 停止录音

5：release 释放资源

2、AudioRecord

AudioRecord 低级API，录制的是PCM数据，没有经过压缩，先看Demo

package com.example.framework;

import java.io.BufferedOutputStream;

import java.io.File;

import java.io.FileOutputStream;

import java.io.IOException;

import android.app.Activity;

import android.media.AudioFormat;

import android.media.AudioRecord;

import android.media.MediaRecorder.AudioSource;

import android.os.Bundle;

public class AudioRecordActivity extends Activity implements Runnable {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

new Thread(this).start();

}

@Override

public void run() {

BufferedOutputStream bos = null;

AudioRecord audioRecord = null;

try {

int audioSource = AudioSource.MIC;

int sampleRateInHz = 44100;

int channelConfig = AudioFormat.CHANNEL_OUT_STEREO;

int audioFormat = AudioFormat.ENCODING_PCM_16BIT;

int bufferSizeInBytes = AudioRecord.getMinBufferSize(sampleRateInHz, channelConfig, audioFormat) * 2;

audioRecord = new AudioRecord(audioSource, sampleRateInHz, channelConfig, audioFormat, bufferSizeInBytes);

audioRecord.startRecording();

bos = new BufferedOutputStream(new FileOutputStream(new File(getCacheDir(), "audio.pcm")));

byte[] buffer = new byte[bufferSizeInBytes];

int len = 0;

while (!isFinishing()) {

len = audioRecord.read(buffer, 0, bufferSizeInBytes);

if (len <= 0) {

break;

}

bos.write(buffer, 0, len);

}

} catch (Exception e) {

e.printStackTrace();

} finally {

if (bos != null) {

try {

bos.close();

} catch (IOException e) {}

}

if (audioRecord != null) {

audioRecord.release();

}

}

}

}上面的代码是录制麦克风的数据，将录制之后的数据写入"audio.pcm" 文件。 AudioRecord 主要参数说明 audioSource 和MediaRecorder的一样。 sampleRateInHz  和MediaRecorder的一样。 channelConfig   和MediaRecorder 不一样，AudioFormat.CHANNEL_OUT_STEREO或者AudioFormat.CHANNEL_OUT_STEREO audioFormat AudioFormat.ENCODING_PCM_8BIT 或者 AudioFormat.ENCODING_PCM_16BIT bufferSizeInBytes 音频缓冲区大小，使用AudioRecord.getMinBufferSize 方法可以获取最小的缓冲区，上面的代码是获取最小的缓冲区乘以2 AudioRecord 的步骤： 1、设置参数 2、startRecording 开始录音 3、read 读取录制的数据 4、release 释放资源 当我们调用startRecording之后就可以调用read方法从系统中读取音频的PCM数据 read方法的返回值：返回的是读取的数据len，如果大于0读取数据成功，否则读取失败. 总结：MediaRecorder 功能比较强大，录制压缩格式，AudioRecord录制的是PCM数据，在实际开发中两个都有可能用到。