Question

In my Application I want to use the AudioTrack class to play back some sound I record. I record the audio via an AudioRecord object, read the object and then I want to play the recorded sound. However, the way I have it programmed now will result in an error in the AudioTrack-JNI which will say that “Buffer direct access is not supported, can’t record”.

The code looks like this:

public class RecorderThread extends Thread{
    private static AudioRecord mAudioRecorder;
    private final int USE_MIC = MediaRecorder.AudioSource.MIC;
    private static final int FREQUENCY = 8000;
    private int mBuffSize, mChannel, mEncoding;
    private byte[] mBuffer;
    private Context mContext;
    private volatile boolean mContinueLoop = true,
                             mDataPresent = false,
                             mProcessData = false;

    private BroadcastReceiver mActionListener = new BroadcastReceiver(){
        @Override
        public void onReceive(Context context, Intent intent){
            if(intent.getAction().equals(mContext.getString(R.string.STOP_THREAD))){
                mContinueLoop = false;
                Thread.currentThread().interrupt();
            } else if(intent.getAction().equals(mContext.getString(R.string.START_RECORDING))){
                mAudioRecorder.startRecording();
            }  else if(intent.getAction().equals(mContext.getString(R.string.STOP_RECORDING))){
                mAudioRecorder.stop();
                mDataPresent = true;
            }  else if(intent.getAction().equals(mContext.getString(R.string.PROCESS_DATA))){
                if(mDataPresent){
                    mProcessData = true;
                    mDataPresent = false;
                }
            }  
        }
    };

    public RecorderThread(Context context){
        mContext = context;
        mChannel = AudioFormat.CHANNEL_IN_MONO;
        mEncoding = AudioFormat.ENCODING_PCM_16BIT;
        mBuffSize = AudioRecord.getMinBufferSize(FREQUENCY, mChannel, mEncoding);
        mBuffer = new byte[FREQUENCY * 10];
        mAudioRecorder = new AudioRecord(USE_MIC, FREQUENCY, mChannel, mEncoding, mBuffer.length);

        IntentFilter filter = new IntentFilter();
        filter.addAction(mContext.getString(R.string.START_RECORDING));
        filter.addAction(mContext.getString(R.string.STOP_RECORDING));
        filter.addAction(mContext.getString(R.string.PROCESS_DATA));
        filter.addAction(mContext.getString(R.string.STOP_THREAD));
        mContext.registerReceiver(mActionListener, filter);
    }

    @Override
    public void run(){
        while(mContinueLoop){
            if(mProcessData){
                // Process data.
                ByteBuffer sampledData = ByteBuffer.wrap(mBuffer);
                int readSamples = mAudioRecorder.read(sampledData, sampledData.limit());
                processData(sampledData, readSamples);
                mProcessData = false;
            }
            try{
                Thread.sleep(100);
            } catch(InterruptedException e){
                e.printStackTrace();
            }
        }
        mAudioRecorder.release();
    }

    private void processData(ByteBuffer sampledData, int readSamples) {
        byte[] data = sampledData.array();
        AudioTrack track = new AudioTrack(AudioManager.STREAM_MUSIC,
                                          FREQUENCY,
                                          AudioFormat.CHANNEL_OUT_MONO,
                                          mEncoding,
                                          data.length,
                                          AudioTrack.MODE_STATIC);
        if(track != null){
            track.write(data, 0, data.length);
            track.play();
            track.release();
        }
    }
}

I’ve looked through the native code that is makes the AudioTrack-JNI (http://www.netmite.com/android/mydroid/1.6/frameworks/base/core/jni/android_media_AudioRecord.cpp), but this doesn’t make it any clearer. The only times this error will pop up is when a buffer capacity <= 0 or when the address to this buffer is null.

So yeah, I’ve got no idea on why this doesn’t work… Anybody with a bit more experience might have… So please enlighten me? Thanks in advance…

Answer 1

I’ve done some more debugging and found that the Issue is not the AudioTrack, but it is with the AudioRecord.read() method. Still haven’t got a solution on it though… Anybody?