在音视频开发中，录音当然是必不可少的。首先我们要学会单独的录音功能，当然这里说的录音是指用AudioRecord来录音，读取录音原始数据，读到的就是所谓的PCM数据。对于录音来说，最重要的几个参数要搞明白：
1、simpleRate采样率，采样率就是采样频率，每秒钟记录多少个样本。
2、channelConfig通道配置，其实就是所谓的单通道，双通道之类的，AudioFormat.CHANNEL_IN_MONO单通道，AudioFormat.CHANNEL_IN_STEREO双通道，这里只列了这两种，还有其它的，可自行查阅。
3、audioFormat音频格式，其实就是采样的精度，每个样本的位数，AudioFormat.ENCODING_PCM_8BIT每个样本占8位，AudioFormat.ENCODING_PCM_16BIT每个样本占16位，这里也只用了这两个，别的没研究。
在学习过程中会用到的一些参数，我这里封装了一个类，如下
public class AudioParams {
enum Format {
SINGLE_8_BIT, DOUBLE_8_BIT, SINGLE_16_BIT, DOUBLE_16_BIT
}
private Format format;
int simpleRate;
AudioParams(int simpleRate, Format f) {
this.simpleRate = simpleRate;
this.format = f;
}
AudioParams(int simpleRate, int channelCount, int bits) {
this.simpleRate = simpleRate;
set(channelCount, bits);
}
int getBits() {
return (format == Format.SINGLE_8_BIT || format == Format.DOUBLE_8_BIT) ? 8 : 16;
}
int getEncodingFormat() {
return (format == Format.SINGLE_8_BIT || format == Format.DOUBLE_8_BIT) ? AudioFormat.ENCODING_PCM_8BIT :
AudioFormat.ENCODING_PCM_16BIT;
}
int getChannelCount() {return (format == Format.SINGLE_8_BIT || format == Format.SINGLE_16_BIT) ? 1 : 2;}
int getChannelConfig() {
return (format == Format.SINGLE_8_BIT || format == Format.SINGLE_16_BIT) ? AudioFormat.CHANNEL_IN_MONO :
AudioFormat.CHANNEL_IN_STEREO;
}
int getOutChannelConfig() {
return (format == Format.SINGLE_8_BIT || format == Format.SINGLE_16_BIT) ? AudioFormat.CHANNEL_OUT_MONO :
AudioFormat.CHANNEL_OUT_STEREO;
}
void set(int channelCount, int bits) {
if ((channelCount != 1 && channelCount != 2) || (bits != 8 && bits != 16)) {
throw new IllegalArgumentException("不支持其它格式 channelCount=$channelCount bits=$bits");
}
if (channelCount == 1) {
if (bits == 8) {
format = Format.SINGLE_8_BIT;
} else {
format = Format.SINGLE_16_BIT;
}
} else {
if (bits == 8) {
format = Format.DOUBLE_8_BIT;
} else {
format = Format.DOUBLE_16_BIT;
}
}
}
}
这里固定使用了单通道8位，双通道8位，单通道16位，双通道16位，所以用了枚举来限制。
为了方便把录音数据拿出来显示、存储，这里写了一个回调方法如下
public interface RecordCallback {
/**
* 数据回调
*
* @param bytes 数据
* @param len 数据有效长度，-1时表示数据结束
*/
void onRecord(byte[] bytes, int len);
}
有了这些参数，现在就可以录音了，先看一下样例
public void startRecord(AudioParams params, RecordCallback callback) {
int simpleRate = params.simpleRate;
int channelConfig = params.getChannelConfig();
int audioFormat = params.getEncodingFormat();
// 根据AudioRecord提供的api拿到最小缓存大小
int bufferSize = AudioRecord.getMinBufferSize(simpleRate, channelConfig, audioFormat);
//创建Record对象
record = new AudioRecord(MediaRecorder.AudioSource.MIC, simpleRate, channelConfig, audioFormat, bufferSize);
recordThread = new Thread(() -> {
byte[] buffer = new byte[bufferSize];
record.startRecording();
recording = true;
while (recording) {
int read = record.read(buffer, 0, bufferSize);
// 将数据回调到外部
if (read > 0 && callback != null) {
callback.onRecord(buffer, read);
}
}
if (callback != null) {
// len 为-1时表示结束
callback.onRecord(buffer, -1);
recording = false;
}
//释放资源
release();
});
recordThread.start();
}
这个方法就是简单的采集音频数据，这个数据就是最原始的pcm数据。
拿到pcm数据以后，如果直接保存到文件是无法直接播放的，因为这只是一堆数据，没有任何格式说明，如果想让普通播放器可以播放，需要在文件中加入文件头，来告诉播放器这个数据的格式，这里是直接保存成wav格式的数据。下面就是加入wav格式文件头的方法
private static byte[] getWaveFileHeader(int totalDataLen, int sampleRate, int channelCount, int bits) {
byte[] header = new byte[44];
// RIFF/WAVE header
header[0] = 'R';
header[1] = 'I';
header[2] = 'F';
header[3] = 'F';
int fileLength = totalDataLen + 36;
header[4] = (byte) (fileLength & 0xff);
header[5] = (byte) (fileLength >> 8 & 0xff);
header[6] = (byte) (fileLength >> 16 & 0xff);
header[7] = (byte) (fileLength >> 24 & 0xff);
//WAVE
header[8] = 'W';
header[9] = 'A';
header[10] = 'V';
header[11] = 'E';
// 'fmt ' chunk
header[12] = 'f';
header[13] = 'm';
header[14] = 't';
header[15] = ' ';
// 4 bytes: size of 'fmt ' chunk
header[16] = 16;
header[17] = 0;
header[18] = 0;
header[19] = 0;
// pcm format = 1
header[20] = 1;
header[21] = 0;
header[22] = (byte) channelCount;
header[23] = 0;
header[24] = (byte) (sampleRate & 0xff);
header[25] = (byte) (sampleRate >> 8 & 0xff);
header[26] = (byte) (sampleRate >> 16 & 0xff);
header[27] = (byte) (sampleRate >> 24 & 0xff);
int byteRate = sampleRate * bits * channelCount / 8;
header[28] = (byte) (byteRate & 0xff);
header[29] = (byte) (byteRate >> 8 & 0xff);
header[30] = (byte) (byteRate >> 16 & 0xff);
header[31] = (byte) (byteRate >> 24 & 0xff);
// block align
header[32] = (byte) (channelCount * bits / 8);
header[33] = 0;
// bits per sample
header[34] = (byte) bits;
header[35] = 0;
//data
header[36] = 'd';
header[37] = 'a';
header[38] = 't';
header[39] = 'a';
header[40] = (byte) (totalDataLen & 0xff);
header[41] = (byte) (totalDataLen >> 8 & 0xff);
header[42] = (byte) (totalDataLen >> 16 & 0xff);
header[43] = (byte) (totalDataLen >> 24 & 0xff);
return header;
}
根据几个参数设置一下文件头，然后直接写入录音采集到的pcm数据，就可被正常播放了。wav文件头格式定义，可点击这里查看或自行百度。
如果想要通过AudioRecord录音直接保存到文件，可参考下面方法
public void startRecord(String filePath, AudioParams params, RecordCallback callback) {
int channelCount = params.getChannelCount();
int bits = params.getBits();
final boolean storeFile = filePath != null && !filePath.isEmpty();
startRecord(params, (bytes, len) -> {
if (storeFile) {
if (file == null) {
File f = new File(filePath);
if (f.exists()) {
f.delete();
}
try {
file = new RandomAccessFile(f, "rw");
file.write(getWaveFileHeader(0, params.simpleRate, channelCount, bits));
} catch (IOException e) {
e.printStackTrace();
}
}
if (len > 0) {
try {
file.write(bytes, 0, len);
} catch (IOException e) {
e.printStackTrace();
}
} else {
try {
// 因为在前面已经写入头信息，所以这里要减去头信息才是数据的长度
int length = (int) file.length() - 44;
file.seek(0);
file.write(getWaveFileHeader(length, params.simpleRate, channelCount, bits));
file.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
if (callback != null) {
callback.onRecord(bytes, len);
}
});
}
先通过RandomAccessFile创建文件，先写入文件头，由于暂时我们不知道会录多长，有多少pcm数据，长度先用0表示，等录音结束后，通过seek(int)方法重新写入文件头信息，也可以先把pcm数据保存到临时文件，然后再写入到一个新的文件中，这里就不举例说明了。
最后放入完整类的代码
package cn.sskbskdrin.record.audio;
import android.media.AudioRecord;
import android.media.MediaRecorder;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
/**
* @author sskbskdrin
* @date 2019/April/3
*/
public class AudioRecordManager {
private AudioParams DEFAULT_FORMAT = new AudioParams(8000, 1, 16);
private AudioRecord record;
private Thread recordThread;
private boolean recording = false;
private RandomAccessFile file;
public void startRecord(String filePath, RecordCallback callback) {
startRecord(filePath, DEFAULT_FORMAT, callback);
}
public void startRecord(String filePath, AudioParams params, RecordCallback callback) {
int channelCount = params.getChannelCount();
int bits = params.getBits();
final boolean storeFile = filePath != null && !filePath.isEmpty();
startRecord(params, (bytes, len) -> {
if (storeFile) {
if (file == null) {
File f = new File(filePath);
if (f.exists()) {
f.delete();
}
try {
file = new RandomAccessFile(f, "rw");
file.write(getWaveFileHeader(0, params.simpleRate, channelCount, bits));
} catch (IOException e) {
e.printStackTrace();
}
}
if (len > 0) {
try {
file.write(bytes, 0, len);
} catch (IOException e) {
e.printStackTrace();
}
} else {
try {
// 因为在前面已经写入头信息，所以这里要减去头信息才是数据的长度
int length = (int) file.length() - 44;
file.seek(0);
file.write(getWaveFileHeader(length, params.simpleRate, channelCount, bits));
file.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
if (callback != null) {
callback.onRecord(bytes, len);
}
});
}
public void startRecord(AudioParams params, RecordCallback callback) {
int simpleRate = params.simpleRate;
int channelConfig = params.getChannelConfig();
int audioFormat = params.getEncodingFormat();
// 根据AudioRecord提供的api拿到最小缓存大小
int bufferSize = AudioRecord.getMinBufferSize(simpleRate, channelConfig, audioFormat);
//创建Record对象
record = new AudioRecord(MediaRecorder.AudioSource.MIC, simpleRate, channelConfig, audioFormat, bufferSize);
recordThread = new Thread(() -> {
byte[] buffer = new byte[bufferSize];
record.startRecording();
recording = true;
while (recording) {
int read = record.read(buffer, 0, bufferSize);
// 将数据回调到外部
if (read > 0 && callback != null) {
callback.onRecord(buffer, read);
}
}
if (callback != null) {
// len 为-1时表示结束
callback.onRecord(buffer, -1);
recording = false;
}
//释放资源
release();
});
recordThread.start();
}
public void stop() {
recording = false;
}
public void release() {
recording = false;
if (record != null) {
record.stop();
record.release();
}
record = null;
file = null;
recordThread = null;
}
private static byte[] getWaveFileHeader(int totalDataLen, int sampleRate, int channelCount, int bits) {
byte[] header = new byte[44];
// RIFF/WAVE header
header[0] = 'R';
header[1] = 'I';
header[2] = 'F';
header[3] = 'F';
int fileLength = totalDataLen + 36;
header[4] = (byte) (fileLength & 0xff);
header[5] = (byte) (fileLength >> 8 & 0xff);
header[6] = (byte) (fileLength >> 16 & 0xff);
header[7] = (byte) (fileLength >> 24 & 0xff);
//WAVE
header[8] = 'W';
header[9] = 'A';
header[10] = 'V';
header[11] = 'E';
// 'fmt ' chunk
header[12] = 'f';
header[13] = 'm';
header[14] = 't';
header[15] = ' ';
// 4 bytes: size of 'fmt ' chunk
header[16] = 16;
header[17] = 0;
header[18] = 0;
header[19] = 0;
// pcm format = 1
header[20] = 1;
header[21] = 0;
header[22] = (byte) channelCount;
header[23] = 0;
header[24] = (byte) (sampleRate & 0xff);
header[25] = (byte) (sampleRate >> 8 & 0xff);
header[26] = (byte) (sampleRate >> 16 & 0xff);
header[27] = (byte) (sampleRate >> 24 & 0xff);
int byteRate = sampleRate * bits * channelCount / 8;
header[28] = (byte) (byteRate & 0xff);
header[29] = (byte) (byteRate >> 8 & 0xff);
header[30] = (byte) (byteRate >> 16 & 0xff);
header[31] = (byte) (byteRate >> 24 & 0xff);
// block align
header[32] = (byte) (channelCount * bits / 8);
header[33] = 0;
// bits per sample
header[34] = (byte) bits;
header[35] = 0;
//data
header[36] = 'd';
header[37] = 'a';
header[38] = 't';
header[39] = 'a';
header[40] = (byte) (totalDataLen & 0xff);
header[41] = (byte) (totalDataLen >> 8 & 0xff);
header[42] = (byte) (totalDataLen >> 16 & 0xff);
header[43] = (byte) (totalDataLen >> 24 & 0xff);
return header;
}
public interface RecordCallback {
/**
* 数据回调
*
* @param bytes 数据
* @param len 数据有效长度，-1时表示数据结束
*/
void onRecord(byte[] bytes, int len);
}
}
如有不对之处还请评论指正
