Android音视频之AudioRecord录音(一)

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