概述
AudioRecord、AudioTrack 的使用都比较简单，基本流程：
AudioRecord：
- AudioRecord.getMinBufferSize()
- new AudioRecord()
- mAudioRecord.read()
如此，即可得到录制好的音频裸数据（PCM）。
AudioTrack 有两种播放方式：
- static：把音频数据一次性写入 AudioTrack，再进行播放
- stream：边写边播
播放流程基本都是：
- AudioTrack.getMinBufferSize()
- new AudioTrack()
- mAudioTrack.write() // static 方式必须先 write，再 play
- mAudioTrack.play()
其中 getMinBufferSize()、new AudioRecord()、new AudioTrack() 需要传入 sampleRate、channel、sampleFormat 等参数，这些参数涉及到音频开发的一些基础知识，可参考我的另一篇博客：音视频开发基础概述 - PCM、YUV、H264、常用软件介绍
AudioRecord 录制 PCM 数据
public class AudioRecorder {
private static final String TAG = "AudioRecorder";
private static final int DEFAULT_SAMPLE_RATE = 48000;
private static final int DEFAULT_PCM_DATA_FORMAT = AudioFormat.ENCODING_PCM_16BIT;
private ExecutorService mExecutor = Executors.newCachedThreadPool();
private AudioRecord mAudioRecord;
private int mBufferSize;
private int mSampleRate = DEFAULT_SAMPLE_RATE;
private int mPcmFormat = DEFAULT_PCM_DATA_FORMAT;
private AudioRecordCallback mRecordCallback;
private Handler mHandler;
private boolean mIsRecording = false;
public void setSampleRate(int sampleRate) {
mSampleRate = sampleRate;
}
public void setPcmFormat(int pcmFormat) {
mPcmFormat = pcmFormat;
}
public void setRecordCallback(AudioRecordCallback recordCallback) {
mRecordCallback = recordCallback;
}
public int getChannels() {
return 1;
}
public boolean start() {
try {
mBufferSize = AudioRecord.getMinBufferSize(mSampleRate, AudioFormat.CHANNEL_IN_MONO,
mPcmFormat);
mAudioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, mSampleRate,
AudioFormat.CHANNEL_IN_MONO, mPcmFormat, mBufferSize);
} catch (Exception e) {
Log.e(TAG, "init AudioRecord exception: " + e.getLocalizedMessage());
return false;
}
if (mAudioRecord.getState() != AudioRecord.STATE_INITIALIZED) {
Log.e(TAG, "cannot init AudioRecord");
return false;
}
mIsRecording = true;
mExecutor.execute(this::record);
mHandler = new Handler(Looper.myLooper());
return true;
}
private void record() {
android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_URGENT_AUDIO);
if (mAudioRecord == null || mAudioRecord.getState() != AudioRecord.STATE_INITIALIZED) {
return;
}
ByteBuffer audioBuffer = ByteBuffer.allocate(mBufferSize);
mAudioRecord.startRecording();
Log.d(TAG, "AudioRecorder started");
int readResult;
while (mIsRecording) {
readResult = mAudioRecord.read(audioBuffer.array(), 0, mBufferSize);
if (readResult > 0 && mRecordCallback != null) {
byte[] data = new byte[readResult];
audioBuffer.position(0);
audioBuffer.limit(readResult);
audioBuffer.get(data, 0, readResult);
mHandler.post(() -> mRecordCallback.onRecordSample(data));
}
}
release();
Log.d(TAG, "AudioRecorder finished");
}
public void stop() {
mIsRecording = false;
}
private void release() {
if (mAudioRecord != null) {
mAudioRecord.stop();
mAudioRecord.release();
mAudioRecord = null;
}
}
public interface AudioRecordCallback {
// start 在哪个线程调用，就运行在哪个线程
void onRecordSample(byte[] data);
}
}
PCM 转 WAV 文件
wav 是一种音频编码算法，它不会压缩音频，其中一种实现是在 PCM 数据前面加上 44 字节，分别描述 PCM 的采样率、声道数、数据格式等信息。
根据 wiki 的描述，wav 文件头如下：
WAV 文件头
代码实现：
private void pcmToWav(File pcmFile, File wavFile) {
FileInputStream fis = null;
FileOutputStream fos = null;
try {
fis = new FileInputStream(pcmFile);
fos = new FileOutputStream(wavFile);
int sampleFormat = mPcmDataFormat == AudioFormat.ENCODING_PCM_16BIT ? 16 : 8;
writeWavHeader(fos, fis.getChannel().size(), sampleFormat, mSampleRate, mChannels);
int channelConfig =mChannels == 1 ? AudioFormat.CHANNEL_IN_MONO : AudioFormat.CHANNEL_IN_STEREO;
int bufferSize = AudioRecord.getMinBufferSize(mSampleRate, channelConfig, mPcmDataFormat);
byte[] data = new byte[bufferSize];
while (fis.read(data) != -1) {
fos.write(data);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (fis != null) {
fis.close();
}
if (fos != null) {
fos.flush();
fos.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
private void writeWavHeader(@NonNull FileOutputStream fos, long pcmDataLength, int sampleFormat,
int sampleRate, int channels) throws IOException {
long audioDataLength = pcmDataLength + 36;
long bitRate = sampleRate * channels * sampleFormat / 8;
byte[] header = new byte[44];
// RIFF
header[0] = 'R';
header[1] = 'I';
header[2] = 'F';
header[3] = 'F';
// pcm data length
header[4] = (byte) (pcmDataLength & 0xff);
header[5] = (byte) ((pcmDataLength >> 8) & 0xff);
header[6] = (byte) ((pcmDataLength >> 16) & 0xff);
header[7] = (byte) ((pcmDataLength >> 24) & 0xff);
// WAVE
header[8] = 'W';
header[9] = 'A';
header[10] = 'V';
header[11] = 'E';
// 'fmt '
header[12] = 'f';
header[13] = 'm';
header[14] = 't';
header[15] = ' ';
header[16] = 16;
header[17] = 0;
header[18] = 0;
header[19] = 0;
// 1(PCM)
header[20] = 1;
header[21] = 0;
// channels
header[22] = (byte) channels;
header[23] = 0;
// sample rate
header[24] = (byte) (sampleRate & 0xff);
header[25] = (byte) ((sampleRate >> 8) & 0xff);
header[26] = (byte) ((sampleRate >> 16) & 0xff);
header[27] = (byte) ((sampleRate >> 24) & 0xff);
// bit rate
header[28] = (byte) (bitRate & 0xff);
header[29] = (byte) ((bitRate >> 8) & 0xff);
header[30] = (byte) ((bitRate >> 16) & 0xff);
header[31] = (byte) ((bitRate >> 24) & 0xff);
header[32] = 4;
header[33] = 0;
// 采样精度
header[34] = (byte) sampleFormat;
header[35] = 0;
// data
header[36] = 'd';
header[37] = 'a';
header[38] = 't';
header[39] = 'a';
// data length
header[40] = (byte) (audioDataLength & 0xff);
header[41] = (byte) ((audioDataLength >> 8) & 0xff);
header[42] = (byte) ((audioDataLength >> 16) & 0xff);
header[43] = (byte) ((audioDataLength >> 24) & 0xff);
fos.write(header);
}
AudioTrack 播放 PCM 数据
private class AudioPlayer {
private AudioTrack mAudioTrack;
private volatile boolean mIsPlaying = false;
private int mBufferSize;
private ExecutorService mExecutor = Executors.newSingleThreadExecutor();
private void start() {
if (!mPcmFile.exists()) {
ToastHelper.show("无音频文件，请先进行录制");
return;
}
if (mIsPlaying) {
ToastHelper.show("当前正在播放中");
return;
}
releaseAudioTrack();
mBufferSize = AudioTrack.getMinBufferSize(mSampleRate, AudioFormat.CHANNEL_OUT_MONO,
mPcmDataFormat);
mAudioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, mSampleRate,
AudioFormat.CHANNEL_OUT_MONO, mPcmDataFormat, mBufferSize, AudioTrack.MODE_STREAM);
mIsPlaying = true;
mExecutor.execute(this::play);
}
private void play() {
Log.d(TAG, "play started");
try {
byte[] buffer = new byte[mBufferSize];
int readCount;
DataInputStream dis = new DataInputStream(new FileInputStream(mPcmFile));
while (dis.available() > 0 && mIsPlaying) {
readCount = dis.read(buffer);
if (readCount == AudioTrack.ERROR_INVALID_OPERATION || readCount == AudioTrack.ERROR_BAD_VALUE) {
continue;
}
if (readCount > 0) {
mAudioTrack.play();
mAudioTrack.write(buffer, 0, readCount);
}
}
mIsPlaying = false;
} catch (IOException e) {
mIsPlaying = false;
Log.e(TAG, "read audio data fail: " + e.getMessage());
}
Log.d(TAG, "play stopped");
}
private void stop() {
mIsPlaying = false;
try {
mExecutor.shutdown();
mExecutor.awaitTermination(500, TimeUnit.MILLISECONDS);
releaseAudioTrack();
} catch (InterruptedException e) {
Log.e(TAG, "stop play faild");
}
}
private void releaseAudioTrack() {
if (mAudioTrack != null) {
mAudioTrack.stop();
mAudioTrack.release();
mAudioTrack = null;
}
}
}
源码已上传到 GitHub
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