Android Audio Record To Wav

I recorded an audio using the audio recorder on Android and it produces a raw PCM file. I'm trying to convert it to a format I can listen to (wav or mp3 for example. I've started

Solution 1:

The only difference between a PCM file and a WAV file is that the PCM file has no header and the WAV file does. The WAV header has key information for playback such as sample rate, number of bits per sample and number of channels. When you load a PCM file either the app has to have prior knowledge of this information or you have to tell it. If you load a PCM file into audacity, for example, it will prompt you to fill in all of that stuff.

In order to make the existing save file a .WAV you need to prepend an appropriate header. I'm not going to go into details about it because there are already many answers on SO detailing it and it is readily available on the web (https://en.wikipedia.org/wiki/WAV)

The second issue you raise about the file length might have something to do with the fact that AudioRecord.read returns an int which is the number of samples actually read as it may be less than you asked for. This is really a second question though

Solution 2:

This is a Sample .WAV Header format Extracted from OMRECORDER:

privatebyte[] wavFileHeader(long totalAudioLen, long totalDataLen, long longSampleRate,
      int channels, long byteRate, byte bitsPerSample) {
    byte[] header = newbyte[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) (channels * (bitsPerSample / 8)); //// block align
    header[33] = 0;
    header[34] = bitsPerSample; // 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);
    return header;
  }

Below is Header format for .aac extracted from WhatsappAudioRecorder:

privatebyte[] createAdtsHeader(int length) {
        int frameLength = length + 7;
        byte[] adtsHeader = newbyte[7];

        adtsHeader[0] = (byte) 0xFF; // Sync Word
        adtsHeader[1] = (byte) 0xF1; // MPEG-4, Layer (0), No CRC
        adtsHeader[2] = (byte) ((MediaCodecInfo.CodecProfileLevel.AACObjectLC - 1) << 6);
        adtsHeader[2] |= (((byte) SAMPLE_RATE_INDEX) << 2);
        adtsHeader[2] |= (((byte) CHANNELS) >> 2);
        adtsHeader[3] = (byte) (((CHANNELS & 3) << 6) | ((frameLength >> 11) & 0x03));
        adtsHeader[4] = (byte) ((frameLength >> 3) & 0xFF);
        adtsHeader[5] = (byte) (((frameLength & 0x07) << 5) | 0x1f);
        adtsHeader[6] = (byte) 0xFC;

        return adtsHeader;
    }