android - 在android中混合音频

Question

我试着点击这个链接:

http://mobilengineering.blogspot.com/2012/06/audio-mix-and-record-in-android.html?showComment=1369622288028#c2333829870074273419

但是混音后，sdcard上的文件(mixed.wav)无法播放，不知道为什么。你能帮助我吗？。非常感谢..

这是我的代码:

公共(public)类 MainActivity 扩展 Activity {

 public static final int FREQUENCY = 44100;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    try {
        mixSound();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

private void mixSound() throws IOException {
    AudioTrack audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, 44100, AudioFormat.CHANNEL_OUT_STEREO, AudioFormat.ENCODING_PCM_16BIT, 44100, AudioTrack.MODE_STREAM);

    InputStream in1 = getResources().openRawResource(R.raw.media_b);
    InputStream in2 = getResources().openRawResource(R.raw.media_c);

    byte[] arrayMusic1 = null;
    arrayMusic1 = new byte[in1.available()];
    arrayMusic1 = createMusicArray(in1);
    in1.close();

    byte[] arrayMusic2 = null;
    arrayMusic2 = new byte[in2.available()];
    arrayMusic2 = createMusicArray(in2);
    in2.close();


    byte[] output = new byte[arrayMusic1.length];

    audioTrack.play();

    for (int i = 0; i < output.length; i++) {
        float samplef1 = arrayMusic1[i] / 128.0f; 
        float samplef2 = arrayMusic2[i] / 128.0f;
        float mixed    = samplef1 + samplef2;

        // reduce the volume a bit:
        mixed *= 0.8;
        // hard clipping
        if (mixed > 1.0f)  mixed = 1.0f;
        if (mixed < -1.0f) mixed = -1.0f;

        byte outputSample = (byte) (mixed * 128.0f);
        output[i]         = outputSample;   
    }

    audioTrack.write(output, 0, output.length);
    convertByteToFile(output);
}

public static byte[] createMusicArray(InputStream is) throws IOException {

    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    byte[] buff = new byte[10240];
    int i = Integer.MAX_VALUE;
    while ((i = is.read(buff, 0, buff.length)) > 0) {
        baos.write(buff, 0, i);
    }

    return baos.toByteArray(); // be sure to close InputStream in calling function

}

public static void convertByteToFile(byte[] fileBytes) throws FileNotFoundException {

    BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(Environment.getExternalStorageDirectory().getPath()+"/mixed.wav"));
    try {
        bos.write(fileBytes);
        bos.flush();
        bos.close();    
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

Answer 1

您输出的只是 PCM 数据。一个有效的 WAV 文件还需要一个 header :

Offset    Size  Name           Description
------------------------------------------------------------------------
0         4     ChunkID        Contains the letters "RIFF" in ASCII form
                               (0x52494646 big-endian form).
4         4     ChunkSize      36 + SubChunk2Size, or more precisely:
                               4 + (8 + SubChunk1Size) + (8 + SubChunk2Size)
                               This is the size of the rest of the chunk 
                               following this number.  This is the size of the 
                               entire file in bytes minus 8 bytes for the
                               two fields not included in this count:
                               ChunkID and ChunkSize.
8         4     Format         Contains the letters "WAVE"
                               (0x57415645 big-endian form).

12        4     Subchunk1ID    Contains the letters "fmt "
                               (0x666d7420 big-endian form).
16        4     Subchunk1Size  16 for PCM.  This is the size of the
                               rest of the Subchunk which follows this number.
20        2     AudioFormat    PCM = 1 (i.e. Linear quantization)
                               Values other than 1 indicate some 
                               form of compression.
22        2     NumChannels    Mono = 1, Stereo = 2, etc.
24        4     SampleRate     8000, 44100, etc.
28        4     ByteRate       == SampleRate * NumChannels * BitsPerSample/8
32        2     BlockAlign     == NumChannels * BitsPerSample/8
                               The number of bytes for one sample including
                               all channels. I wonder what happens when
                               this number isn't an integer?
34        2     BitsPerSample  8 bits = 8, 16 bits = 16, etc.
          2     ExtraParamSize if PCM, then doesn't exist
          X     ExtraParams    space for extra parameters

36        4     Subchunk2ID    Contains the letters "data"
                               (0x64617461 big-endian form).
40        4     Subchunk2Size  == NumSamples * NumChannels * BitsPerSample/8
                               This is the number of bytes in the data.
                               You can also think of this as the size
                               of the read of the subchunk following this 
                               number.

在此之后写入 PCM 数据。

(Reference)。