Android: AudioRecord a wave, mono file

Question

I want record sound for android app, in wave format,16bits/mono (1 channel). I used this code:

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;
            }
            }
        }
    }; 

but the record is always a stereo channels, 32 bit. I used AudioFormat.CHANNEL_IN_MONO and AudioFormat.ENCODING_PCM_16BIT.

Can someone help me?

Answer 1

Seems like your header contains an error:

header[32] = (byte) (2 * 16 / 8);  // block align

it should be

header[32] = (byte) (1 * 16 / 8);  // block align

this should be channels*RECORDER_BPP/8

I've tried it and it seems to work.

Answer 2

According to what was discussed in the comments, if you're getting a 528 kb file from ~3 seconds of audio, then 1 of two things is happening. Either you're recording in stereo (seems to be the more likely of the two if you say you're seeing two channels in audacity and since 32bit PCM encoding isn't supported in android) or you're recording in 32 bits sample with one channel. It's strange that audacity would tell you that the file sample size is 32 bits/sample.

My reasoning for this is that

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

Since you properly setup your audioRecorder object, I'm not sure where the second channel is coming form. I'd recommend manipulating the values in the byteRate long in the copyWaveFile method and seeing the effects that has on your audio files.