android - Android:播放PCM文件时出错

Question

我正在尝试播放从麦克风录制音频时创建的PCM文件。

我使用AudioRecord是因为我想分析麦克风记录的声音的频率。

播放PCM文件的代码段如下。但是，当我尝试播放文件时，正在播放很大的声音。

FileInputStream fis=null;
    File l=null;
    l=new File(Environment.getExternalStorageDirectory().getAbsolutePath()+"/Notate/f1.pcm");

    byte[] buffer=new byte[(int)l.length()];

    try {
        fis = new FileInputStream(Environment.getExternalStorageDirectory().getAbsolutePath() + "/Notate/f1.pcm");
        fis.read(buffer);
    }
    catch(Exception e)
    {

    }
    int intSize = android.media.AudioTrack.getMinBufferSize(44100, AudioFormat.CHANNEL_OUT_MONO,
            AudioFormat.ENCODING_PCM_16BIT);
    AudioTrack at = new AudioTrack(AudioManager.STREAM_MUSIC, 44100, AudioFormat.CHANNEL_OUT_MONO,
            AudioFormat.ENCODING_PCM_16BIT, intSize, AudioTrack.MODE_STREAM);
    if (at!=null) {
        at.play();
        at.write(buffer, 0, buffer.length);
        at.stop();
        at.release();
    }

下面是用于存储PCM文件的代码。

private class RecordAudio extends AsyncTask<Void, Double, Void> {
    FileOutputStream os = null;
    BufferedOutputStream bos =null;
    DataOutputStream dos = null;
    @Override
    protected Void doInBackground(Void... params) {
        int bufferSize = AudioRecord.getMinBufferSize(sampleRate, channelConfig, audioEncoding);                // Gets the minimum buffer needed
        AudioRecord audioRecord = new AudioRecord(audioSource, sampleRate, channelConfig, audioEncoding, bufferSize);   // The RAW PCM sample recording
        File f=new File(Environment.getExternalStorageDirectory().getAbsolutePath()+"/Notate/");
        if(!f.isDirectory()) {
            File newDirectory = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/Notate/");
            newDirectory.mkdirs();
        }
        String filepath=Environment.getExternalStorageDirectory().getAbsolutePath()+"/Notate/f1.pcm";
        short[] buffer = new short[blockSize];          // Save the raw PCM samples as short bytes
        try{
            os=new FileOutputStream(filepath);
        }
        catch(FileNotFoundException e)
        {

        }
        bos = new BufferedOutputStream(os);
        dos = new DataOutputStream(bos);
        try {
            audioRecord.startRecording();  //Start
        } catch (Throwable t) {
        }
        while (started) {
            int length=audioRecord.read(buffer, 0, blockSize);

            Yin alpha = new Yin(44100, 1024, 0.2);
            float[] floaters = new float[buffer.length];
            for (int i = 0; i < buffer.length; i++) {
                floaters[i] = buffer[i];
            }
            for(int k=0;k<length;k++) {
                try {
                    dos.writeShort(buffer[k]);


                } catch (IOException e) {

                }
            }
            float result = alpha.getPitch(floaters);
            publishProgress((double) result);

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

        return null;
    }

Answer 1

writeShort以大尾数格式(即最高有效字节在前)写入值，而AudioTrack可能期望样本为小尾数(最低有效字节在前)。

如果在录制时使用byte[]而不是short[]，则会使事情变得更简单。然后，您可以简单地使用DataOutputStream写入dos.write(buffer, 0, length);。在这种情况下，您必须对转换为浮点值进行一些修改:

for (int i = 0; i < length; i += 2) {
    floaters[i] = (short)(buffer[i] | (buffer[i+1] << 8));
}