android - AudioRecord 启动后返回一些空数据

Question

我编写了一个标准代码，用于使用 AudioRecord 从麦克风接收数据。这是我的代码:

AudioReceiver() {
    int minHardwareBufferSize = AudioRecord.getMinBufferSize(SAMPLE_RATE,
            CHANNEL_CONFIG, AUDIO_FORMAT);
    Log.d(TAG, "minHardwareBufferSize = " + minHardwareBufferSize);
    int bufferSizeBytes = (minHardwareBufferSize > MIN_BUFFER_SIZE_BYTES) ?
            minHardwareBufferSize : MIN_BUFFER_SIZE_BYTES;
    bufferSizeShorts = bufferSizeBytes / 2;

    //резервируем буфер с запасом в 2 раза
    audioRecorder = new AudioRecord(MediaRecorder.AudioSource.MIC,
            SAMPLE_RATE, CHANNEL_CONFIG, AUDIO_FORMAT, bufferSizeBytes * 2);

    testStack = new short[bufferSizeShorts * 4];
    Arrays.fill(testStack, (short) 2000);
}


boolean startReceive() {
    audioRecorder.startRecording();
    isReceiving = true;
    int recordingState = audioRecorder.getRecordingState();
    Log.d(TAG, "recordingState = " + recordingState);
    new Thread(receivingRunnable).start();
    return (recordingState == AudioRecord.RECORDSTATE_RECORDING);
}


boolean stopReceive() {
    isReceiving = false;
    audioRecorder.stop();
    int recordingState = audioRecorder.getRecordingState();
    Log.d(TAG, "recordingState = " + recordingState);
    return (recordingState == AudioRecord.RECORDSTATE_STOPPED);
}


private Runnable receivingRunnable = new Runnable() {
    @Override
    public void run() {
        int readCount = 0;
        short[] dataBuffer = new short[bufferSizeShorts];
        while (isReceiving) {
            testBusy = true;
            for (int j = 0; j < 4; j++) {
                readCount = audioRecorder.read(dataBuffer, 0, dataBuffer.length);
                Log.d(TAG, "receive " + readCount + " bytes");
                System.arraycopy(dataBuffer, 0, testStack, bufferSizeShorts * j, readCount);
            }
            isReceiving = false;
            testBusy = false;
        }
    }
};

但我注意到，在 startReceive 函数第一次启动后，在 testStack 缓冲区的开头，有空数据(Nexus 4 上大约有 1000 个样本，见数据图)。

从初始化 AudioReceiver 到启动 startReceive 需要很长时间。问题的原因可能是什么？

Answer 1

似乎延迟是由于操作系统需要时间对数据重新采样而导致的，而且很难对所有设备采用一个采样率。 other posts 也提到了.因此，我改为将音频记录逻辑移至 Activity onCreate。当我不需要音频或音频暂停时，我就丢弃数据。

当我一直在录音时，我没有观察到电池电量耗尽。虽然这可能不是解决此问题的最佳方法，但这对我来说绝对是一个可以接受的解决方法。