音视频学习系列第（二）篇---音频采集和播放

音视频系列

音频采集AudioRecord

AudioRecord与MediaRecorder区别
前者采集的是原始的音频数据，后者会对音频数据进行编码压缩并存储成文件

AudioRecord的使用

1.AudioRecord参数配置

public AudioRecord(int audioSource, int sampleRateInHz, int channelConfig, int audioFormat, int bufferSizeInBytes) 

audioSource
音频采集的输入源，可选值在MediaRecorder.AudioSource中以常量值定义，如

public static final int MIC = 1; //表示手机麦克风输入 

sampleRateInHz
采样率，录音设备1S内对声音信号的采集次数，单位Hz，目前44100Hz是惟一能够保证兼容全部Android手机的采样率。
背景知识
Hz，物质在1S内周期性变化的次数
咱们知道人耳能听到的声音频率范围在20Hz到20KHz之间，为了避免失真，采样频率应该在40KHz以上

channelConfig
通道数的配置，可选值在AudioFormat中以常量值定义，经常使用的以下

public static final int CHANNEL_IN_LEFT = 0x4; public static final int CHANNEL_IN_RIGHT = 0x8; public static final int CHANNEL_IN_FRONT = 0x10; //单通道 public static final int CHANNEL_IN_MONO = CHANNEL_IN_FRONT; //双通道 public static final int CHANNEL_IN_STEREO = (CHANNEL_IN_LEFT | CHANNEL_IN_RIGHT); 

audioFormat
用来配置数据位宽，可选值在可选值在AudioFormat中以常量值定义，经常使用的以下

public static final int ENCODING_PCM_16BIT = 2; public static final int ENCODING_PCM_8BIT = 3; 

背景知识
PCM经过抽样、量化、编码三个步骤将连续变化的模拟信号转换为数字编码。

bufferSizeInBytes
配置的是AudioRecord内部音频缓冲区的大小，该值不能低于一帧音频帧的大小，一帧音频帧的大小计算以下
int size=采样率 * 采样时间 * 位宽 * 通道数
其中采样时间通常取2.5ms~120ms，具体取多少由厂商或者应用决定
每一帧采样的时间越短，产生的延时越小，但碎片化的数据也会越多
在Android开发中，应该使用AudioRecord类中的方法

static public int getMinBufferSize(int sampleRateInHz, int channelConfig, int audioFormat) 

来计算音频缓冲区的大小

2.音频采集方法

audioRecord.startRecording();   //开始录制 audioRecord.stop(); //中止录制 audioRecord.read(bytes,0,bytes.length); //读取录音数据 

3.示例代码

<uses-permission android:name="android.permission.RECORD_AUDIO"/> 

而且该权限属于危险权限，须要动态获取权限

public class AudioCapture { private static final String TAG = "AudioCapture"; private final int DEFAULT_SOURCE = MediaRecorder.AudioSource.MIC; //麦克风 private final int DEFAULT_RATE = 44100; //采样率 private final int DEFAULT_CHANNEL = AudioFormat.CHANNEL_IN_STEREO; //双通道(左右声道) private final int DEFAULT_FORMAT = AudioFormat.ENCODING_PCM_16BIT; //数据位宽16位 private AudioRecord mAudioRecord; private int mMinBufferSize; private onAudioFrameCaptureListener mOnAudioFrameCaptureListener; private boolean isRecording = false; public void startRecord() { startRecord(DEFAULT_SOURCE, DEFAULT_RATE, DEFAULT_CHANNEL, DEFAULT_FORMAT); } public void startRecord(int audioSource, int sampleRateInHz, int channelConfig, int audioFormat) { mMinBufferSize = AudioRecord.getMinBufferSize(sampleRateInHz, channelConfig, audioFormat); if (mMinBufferSize == AudioRecord.ERROR_BAD_VALUE) { Log.d(TAG, "Invalid parameter"); return; } mAudioRecord = new AudioRecord(audioSource, sampleRateInHz, channelConfig, audioFormat, mMinBufferSize); if (mAudioRecord.getState() == AudioRecord.STATE_UNINITIALIZED) { Log.d(TAG, "AudioRecord initialize fail"); return; } mAudioRecord.startRecording(); isRecording = true; CaptureThread t = new CaptureThread(); t.start(); Log.d(TAG, "AudioRecord Start"); } public void stopRecord() { isRecording = false; if (mAudioRecord.getRecordingState() == AudioRecord.RECORDSTATE_RECORDING) { mAudioRecord.stop(); } mAudioRecord.release(); mOnAudioFrameCaptureListener = null; Log.d(TAG, "AudioRecord Stop"); } private class CaptureThread extends Thread { @Override public void run() { while (isRecording) { byte[] buffer = new byte[mMinBufferSize]; int result = mAudioRecord.read(buffer, 0, buffer.length); Log.d(TAG, "Captured " + result + " byte"); if (mOnAudioFrameCaptureListener != null) { mOnAudioFrameCaptureListener.onAudioFrameCapture(buffer); } } } } public interface onAudioFrameCaptureListener { void onAudioFrameCapture(byte[] audioData); } public void setOnAudioFrameCaptureListener(onAudioFrameCaptureListener listener) { mOnAudioFrameCaptureListener = listener; } } 

调用方式

audioCapture=new AudioCapture(); audioCapture.startRecord(); 

音频播放AudioTrack

AudioTrack，MediaPlayer，SoundPool的区别

mediaplayer适合长时间播放音乐
soundpool适合短期的音频片断，如游戏声音，按键声音
audiotrack更接近底层，更灵活，播放的是pcm音频数据

AudioTrack的使用

1.AudioTrack参数配置

public AudioTrack(int streamType, int sampleRateInHz, int channelConfig, int audioFormat, int bufferSizeInBytes, int mode) 

streamType
音频管理策略，如咱们在小米手机调节音量时，会出现3种声音调节的类型，音乐，铃声，闹钟
该参数的可选值在AudioManager类中，如：

STREAM_MUSCI：音乐声
STREAM_RING：铃声
STREAM_NOTIFICATION：通知声

sampleRateInHz
采样率，看源码知道，范围在4000~192000

public static final int SAMPLE_RATE_HZ_MIN = 4000; public static final int SAMPLE_RATE_HZ_MAX = 192000; 

channelConfig
通道数的配置，可选值在AudioFormat中以常量值定义，经常使用的以下

public static final int CHANNEL_IN_LEFT = 0x4; public static final int CHANNEL_IN_RIGHT = 0x8; public static final int CHANNEL_IN_FRONT = 0x10; //单通道 public static final int CHANNEL_IN_MONO = CHANNEL_IN_FRONT; //双通道 public static final int CHANNEL_IN_STEREO = (CHANNEL_IN_LEFT | CHANNEL_IN_RIGHT); 

audioFormat
用来配置数据位宽，可选值在可选值在AudioFormat中以常量值定义，经常使用的以下

public static final int ENCODING_PCM_16BIT = 2; public static final int ENCODING_PCM_8BIT = 3; 

bufferSizeInBytes
配置的是AudioTrack内部音频缓冲区的大小，一样AudioTrack提供了获取缓冲区大小的方法

AudioTrack.getMinBufferSize(sampleRateInHz, channelConfig, audioFormat); 

mode
AudioTrack有两种播放方式 MODE_STATIC和MODE_STREAM
前者是一次性将全部数据写入播放缓冲区，而后播放
后者是一边写入一边播放

2.音频播放方法

mAudioTrack.play();  //开始播放 mAudioTrack.stop(); //中止播放 mAudioTrack.write(audioData,offsetInBytes,sizeInBytes);//将pcm数据写入缓冲区 

3.示例代码

public class AudioPlayer { private static final String TAG = "AudioPlayer"; private final int DEFAULT_STREAM_TYPE = AudioManager.STREAM_MUSIC; //流音乐 private final int DEFAULT_RATE = 44100; //采样率 private final int DEFAULT_CHANNEL = AudioFormat.CHANNEL_IN_STEREO; //双通道(左右声道) private final int DEFAULT_FORMAT = AudioFormat.ENCODING_PCM_16BIT; //数据位宽16位 private static final int DEFAULT_PLAY_MODE = AudioTrack.MODE_STREAM; private AudioTrack mAudioTrack; private int mMinBufferSize; private boolean isPlaying=false; public void startPlay(){ startPlay(DEFAULT_STREAM_TYPE,DEFAULT_RATE,DEFAULT_CHANNEL,DEFAULT_FORMAT); } public void startPlay(int streamType, int sampleRateInHz, int channelConfig, int audioFormat){ if(isPlaying){ Log.d(TAG,"AudioPlayer has played"); return; } mMinBufferSize = AudioTrack.getMinBufferSize(sampleRateInHz, channelConfig, audioFormat); if (mMinBufferSize == AudioRecord.ERROR_BAD_VALUE) { Log.d(TAG, "Invalid parameter"); return; } mAudioTrack=new AudioTrack(streamType,sampleRateInHz,channelConfig,audioFormat, mMinBufferSize,DEFAULT_PLAY_MODE); if(mAudioTrack.getState()==AudioTrack.STATE_UNINITIALIZED){ Log.d(TAG, "AudioTrack initialize fail"); return; } isPlaying=true; } public void stopPlay(){ if(!isPlaying){ Log.d(TAG, "AudioTrack is not playing"); return; } if(mAudioTrack.getPlayState()==AudioTrack.PLAYSTATE_PLAYING){ mAudioTrack.stop(); } mAudioTrack.release(); isPlaying=false; } private void play(byte[] audioData,int offsetInBytes, int sizeInBytes){ if(!isPlaying){ Log.d(TAG, "AudioTrack not start"); return; } if(sizeInBytes<mMinBufferSize){ Log.d(TAG, "audio data not enough"); //return; } if(mAudioTrack.write(audioData,offsetInBytes,sizeInBytes)!=mMinBufferSize){ Log.d(TAG, "AudioTrack can not write all the data"); } mAudioTrack.play(); Log.d(TAG, "played "+sizeInBytes+" bytes"); } } 

测试

//原始音频的录入和播放 public class AudioPCMActivity extends DemoActivity { private Button btn_audio_record; private Button btn_audio_record_play; private AudioCapture audioCapture; private AudioPlayer audioPlayer; private PcmFileWriter pcmFileWriter; private PcmFileReader pcmFileReader; private boolean isReading; private String path=""; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { setContentView(R.layout.activity_media_audio); super.onCreate(savedInstanceState); } @Override public void initHead() { } @Override public void initView() { btn_audio_record=findViewById(R.id.btn_audio_record); btn_audio_record_play=findViewById(R.id.btn_audio_record_play); } @Override public void initData() { path=FileUtil.getAudioDir(this)+"/audioTest.pcm"; audioCapture=new AudioCapture(); audioPlayer=new AudioPlayer(); pcmFileReader=new PcmFileReader(); pcmFileWriter=new PcmFileWriter(); String des = "录音权限被禁止，咱们须要打开录音权限"; String[] permissions = new String[]{Manifest.permission.RECORD_AUDIO}; baseAt.requestPermissions(des, permissions, 100, new PermissionsResultListener() { @Override public void onPermissionGranted() { } @Override public void onPermissionDenied() { finish(); } }); } @Override public void initEvent() { btn_audio_record.setOnTouchListener(new View.OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { if(event.getAction()==MotionEvent.ACTION_DOWN){ Log.d("TAG","按住"); start(); }else if(event.getAction()==MotionEvent.ACTION_UP){ Log.d("TAG","松开"); stop(); } return false; } }); btn_audio_record_play.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { play(); } }); } //播放录音 private void play(){ isReading=true; pcmFileReader.openFile(path); audioPlayer.startPlay(); new AudioTrackThread().start(); } private class AudioTrackThread extends Thread{ @Override public void run() { byte[] buffer = new byte[1024]; while (isReading && pcmFileReader.read(buffer,0,buffer.length)>0){ audioPlayer.play(buffer,0,buffer.length); } audioPlayer.stopPlay(); pcmFileReader.closeFile(); } } //开始录音 private void start(){ pcmFileWriter.openFile(path); btn_audio_record.setText("松开 结束"); audioCapture.startRecord(); audioCapture.setOnAudioFrameCaptureListener(new AudioCapture.onAudioFrameCaptureListener() { @Override public void onAudioFrameCapture(byte[] audioData) { pcmFileWriter.write(audioData,0,audioData.length); } }); } //结束录音 private void stop(){ btn_audio_record.setText("按住 录音"); audioCapture.stopRecord(); pcmFileWriter.closeFile(); } } 

github 测试代码在com.sf.sofarmusic.demo.media下 其余代码在libplayer模块中