Android：录制和收听音频

Question

I try to implement a record and listen a audio from differents post, but I have a delay for 40 ms.

This is my code.

public class record {
    private AudioRecord recorder = null;
    private boolean isRecording = false;
    private int SAMPLERATE = 8000;
    private int CHANNELS = AudioFormat.CHANNEL_CONFIGURATION_MONO;
    private int AUDIO_FORMAT = AudioFormat.ENCODING_PCM_16BIT;
    private int bufferSize = AudioRecord.getMinBufferSize(SAMPLERATE, CHANNELS,
                    AUDIO_FORMAT);
    private Thread recordingThread = null;

    public void startRecording() {
            recorder = new AudioRecord(MediaRecorder.AudioSource.MIC, SAMPLERATE,
                            CHANNELS, AUDIO_FORMAT, bufferSize);

            recorder.startRecording();
            isRecording = true;

            recordingThread = new Thread(new Runnable()

            {
                    public void run() {
                            writeAudioData();
                    }

            });
            recordingThread.start();

    }

    public void stopRecording() {
            isRecording = false;
            recorder.stop();
            recorder.release();
            recorder = null;
            recordingThread = null;
    }

    private void writeAudioData() {

            byte data[] = new byte[bufferSize];

            int buff = 8000;
            int minBufferSize = AudioTrack.getMinBufferSize(buff,
                            AudioFormat.CHANNEL_CONFIGURATION_MONO,
                            AudioFormat.ENCODING_PCM_16BIT);

            Log.i("AUDIO", "BufferSize:" + minBufferSize);

            AudioTrack at = new AudioTrack(AudioManager.STREAM_MUSIC, buff,
                            AudioFormat.CHANNEL_CONFIGURATION_MONO,
                            AudioFormat.ENCODING_PCM_16BIT, minBufferSize,
                            AudioTrack.MODE_STREAM);

            at.play();

            while (isRecording) {
                    recorder.read(data, 0, bufferSize);
                    at.write(data, 0, bufferSize);
            }
            at.stop();
            at.release();
    }

}

How can I reduce the delay?. I try reducing the buffer, but the problem still continue.

Answer 1

Depending on the measurement object and method, there could be tens of milliseconds delay or hundreds milliseconds delay in Android audio system.

If measuring the delay between the playing and the recording, 40ms delay is a normal value, actually I see 30~50ms delay value in my this test on Android 4.4.3:

https://github.com/garyyu/AudioTracker-Test

Also, if you check your printed "minBufferSize" value, you will find this minimum buffer size is 40ms (on my Nexus7 2013). And there's frame delay when you play, we can't expect the immediate playing when calling "at.write()", I guess internally there's another buffer to store your "writing" data. And same in the recording side. So there're much more delay than 40ms if measuring from the playing start function call to the real sound output.
If need more suggestion, you need describe the detail about how do you measure your delay.