Android: AudioRecord a wave, mono 文件

Question

我想为 Android 应用录制声音，波形格式，16 位/单声道(1 声道)。我使用了这段代码:

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import android.app.Activity;
import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.Button;

public class MainActivity extends ActionBarActivity {

    private static final int RECORDER_BPP = 16;
    private static final String AUDIO_RECORDER_FILE_EXT_WAV = ".wav";
    private static final String AUDIO_RECORDER_FOLDER = "AudioRecorder";
    private static final String AUDIO_RECORDER_TEMP_FILE = "record_temp.raw";
    private static final int RECORDER_SAMPLERATE = 44100;
    private static final int RECORDER_CHANNELS = AudioFormat.CHANNEL_IN_MONO;
    private static final int RECORDER_AUDIO_ENCODING = AudioFormat.ENCODING_PCM_16BIT;

    private AudioRecord recorder = null;
    private int bufferSize = 0;
    private Thread recordingThread = null;
    private boolean isRecording = false;

    @SuppressWarnings("deprecation")
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_main);

        setButtonHandlers();
        enableButtons(false);

        bufferSize = AudioRecord.getMinBufferSize(8000,AudioFormat.CHANNEL_IN_MONO,AudioFormat.ENCODING_PCM_16BIT);
    }

    private void setButtonHandlers() {
        ((Button)findViewById(R.id.btnStart)).setOnClickListener(btnClick);
        ((Button)findViewById(R.id.btnStop)).setOnClickListener(btnClick);
    }

    private void enableButton(int id,boolean isEnable){
        ((Button)findViewById(id)).setEnabled(isEnable);
    }

    private void enableButtons(boolean isRecording) {
        enableButton(R.id.btnStart,!isRecording);
        enableButton(R.id.btnStop,isRecording);
    }

    private String getFilename(){
        String filepath = Environment.getExternalStorageDirectory().getPath();
        File file = new File(filepath,AUDIO_RECORDER_FOLDER);

        if(!file.exists()){
            file.mkdirs();
        }

        return (file.getAbsolutePath() + "/" + System.currentTimeMillis() + AUDIO_RECORDER_FILE_EXT_WAV);
    }

    private String getTempFilename(){
        String filepath = Environment.getExternalStorageDirectory().getPath();
        File file = new File(filepath,AUDIO_RECORDER_FOLDER);

        if(!file.exists()){
            file.mkdirs();
        }

        File tempFile = new File(filepath,AUDIO_RECORDER_TEMP_FILE);

        if(tempFile.exists())
            tempFile.delete();

        return (file.getAbsolutePath() + "/" + AUDIO_RECORDER_TEMP_FILE);
    }

    private void startRecording(){
        recorder = new AudioRecord(MediaRecorder.AudioSource.MIC,
                RECORDER_SAMPLERATE, RECORDER_CHANNELS,RECORDER_AUDIO_ENCODING, bufferSize);

        int i = recorder.getState();
        if(i==1)
            recorder.startRecording();

        isRecording = true;

        recordingThread = new Thread(new Runnable() {

            @Override
            public void run() {
                writeAudioDataToFile();
            }
        },"AudioRecorder Thread");

        recordingThread.start();
    }

    private void writeAudioDataToFile(){
        byte data[] = new byte[bufferSize];
        String filename = getTempFilename();
        FileOutputStream os = null;

        try {
            os = new FileOutputStream(filename);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        int read = 0;

        if(null != os){
            while(isRecording){
                read = recorder.read(data, 0, bufferSize);

                if(AudioRecord.ERROR_INVALID_OPERATION != read){
                    try {
                        os.write(data);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }

            try {
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private void stopRecording(){
        if(null != recorder){
            isRecording = false;

            int i = recorder.getState();
            if(i==1)
                recorder.stop();
            recorder.release();

            recorder = null;
            recordingThread = null;
        }

        copyWaveFile(getTempFilename(),getFilename());
        deleteTempFile();
    }

    private void deleteTempFile() {
        File file = new File(getTempFilename());

        file.delete();
    }

    private void copyWaveFile(String inFilename,String outFilename){
        FileInputStream in = null;
        FileOutputStream out = null;
        long totalAudioLen = 0;
        long totalDataLen = totalAudioLen + 36;
        long longSampleRate = RECORDER_SAMPLERATE;
        int channels = 1;
        long byteRate = RECORDER_BPP * RECORDER_SAMPLERATE * channels/8;

        byte[] data = new byte[bufferSize];

        try {
            in = new FileInputStream(inFilename);
            out = new FileOutputStream(outFilename);
            totalAudioLen = in.getChannel().size();
            totalDataLen = totalAudioLen + 36;

            // AppLog.logString("File size: " + totalDataLen);

            WriteWaveFileHeader(out, totalAudioLen, totalDataLen,
                    longSampleRate, channels, byteRate);

            while(in.read(data) != -1){
                out.write(data);
            }

            in.close();
            out.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void WriteWaveFileHeader(
            FileOutputStream out, long totalAudioLen,
            long totalDataLen, long longSampleRate, int channels,
            long byteRate) throws IOException {

        byte[] header = new byte[44];

        header[0] = 'R';  // RIFF/WAVE header
        header[1] = 'I';
        header[2] = 'F';
        header[3] = 'F';
        header[4] = (byte) (totalDataLen & 0xff);
        header[5] = (byte) ((totalDataLen >> 8) & 0xff);
        header[6] = (byte) ((totalDataLen >> 16) & 0xff);
        header[7] = (byte) ((totalDataLen >> 24) & 0xff);
        header[8] = 'W';
        header[9] = 'A';
        header[10] = 'V';
        header[11] = 'E';
        header[12] = 'f';  // 'fmt ' chunk
        header[13] = 'm';
        header[14] = 't';
        header[15] = ' ';
        header[16] = 16;  // 4 bytes: size of 'fmt ' chunk
        header[17] = 0;
        header[18] = 0;
        header[19] = 0;
        header[20] = 1;  // format = 1
        header[21] = 0;
        header[22] = (byte) channels;
        header[23] = 0;
        header[24] = (byte) (longSampleRate & 0xff);
        header[25] = (byte) ((longSampleRate >> 8) & 0xff);
        header[26] = (byte) ((longSampleRate >> 16) & 0xff);
        header[27] = (byte) ((longSampleRate >> 24) & 0xff);
        header[28] = (byte) (byteRate & 0xff);
        header[29] = (byte) ((byteRate >> 8) & 0xff);
        header[30] = (byte) ((byteRate >> 16) & 0xff);
        header[31] = (byte) ((byteRate >> 24) & 0xff);
        header[32] = (byte) (2 * 16 / 8);  // block align
        header[33] = 0;
        header[34] = RECORDER_BPP;  // bits per sample
        header[35] = 0;
        header[36] = 'd';
        header[37] = 'a';
        header[38] = 't';
        header[39] = 'a';
        header[40] = (byte) (totalAudioLen & 0xff);
        header[41] = (byte) ((totalAudioLen >> 8) & 0xff);
        header[42] = (byte) ((totalAudioLen >> 16) & 0xff);
        header[43] = (byte) ((totalAudioLen >> 24) & 0xff);

        out.write(header, 0, 44);
    }

    private View.OnClickListener btnClick = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            switch(v.getId()){
            case R.id.btnStart:{
                //  AppLog.logString("Start Recording");

                enableButtons(true);
                startRecording();

                break;
            }
            case R.id.btnStop:{
                //     AppLog.logString("Start Recording");

                enableButtons(false);
                stopRecording();

                break;
            }
            }
        }
    }; 

但记录始终是立体声 channel ，32 位。我使用了 AudioFormat.CHANNEL_IN_MONO 和 AudioFormat.ENCODING_PCM_16BIT。

有人可以帮助我吗？

Answer 1

根据评论中讨论的内容，如果您从约 3 秒的音频中获得 528 kb 的文件，则两种情况中的一种正在发生。要么你正在以立体声录制(如果你说你在大胆中看到两个 channel 并且因为 android 不支持 32 位 PCM 编码，那么这两个 channel 似乎更有可能)或者你正在以 32 位样本录制一个 channel 。奇怪的是，audacity 会告诉您文件样本大小为 32 位/样本。

我的理由是

(44100 hz * 3 seconds * 32 bits/sample) = 528 kb 
and
2 channels * (44100 hz * 3 seconds * 16 bits/sample) = 528 kb

由于您正确设置了 audioRecorder 对象，我不确定第二个 channel 来自哪里。我建议在 copyWaveFile 方法中操作 byteRate long 中的值并查看对音频文件的影响。