音频记录缓冲区大小

Question

我按如下方式初始化 AudioRecord 实例：

// TODO: remember to add RECORD_AUDIO permission
int audioSource = MediaRecorder.AudioSource.MIC;

// TODO: I should consider Nyquist frequency and tell the user if her device can correctly detect frequencies in the range of her instrument
int sampleRateInHz = getDeviceSampleRate(context);

int channelConfig = AudioFormat.CHANNEL_IN_MONO;
int audioFormat = AudioFormat.ENCODING_PCM_16BIT;

// TODO: bufferSizeInBytes should be set according to minimum detectable frequency in order to have at least three periods
int bufferSizeInBytes = AudioRecord.getMinBufferSize(sampleRateInHz, channelConfig, audioFormat);

AudioRecord audioRecord = new AudioRecord(audioSource, sampleRateInHz, channelConfig, audioFormat, bufferSizeInBytes);

这是我的问题：

我必须从缓冲区读取短裤，因为我指定了 ENCODING_PCM_16BIT。正确吗？
如果以字节为单位的最小缓冲区大小为 1000，我将有 500 个短裤。因此，如果我需要 4096 个样本，我必须将 bufferSizeInBytes 设置为 8192。是否正确？

谢谢。

Answer 1

I have to read shorts from the buffer because I specified ENCODING_PCM_16BIT. Is it correct?

你应该，但你不一定必须。您可以将示例读入 byte[]，但是在将 byte 转换为 short 时，由您来处理字节顺序。

If minimum buffer size in bytes is 1000 I'll have 500 shorts. So if I need 4096 samples I have to set bufferSizeInBytes to 8192. Is it correct?

实际上，没有。

最小缓冲区大小是 AudioRecord 实例可以接受的最小大小。这就像一个门槛。 AudioRecord constructor documentation 说：

Using values smaller than getMinBufferSize() will result in an initialization failure.

在某些情况下，您可能希望使用比最小值更大的缓冲区大小。 AudioRecord.getMinBufferSize() documentation` 说：

Note that this size doesn't guarantee a smooth recording under load, and higher values should be chosen according to the expected frequency at which the AudioRecord instance will be polled for new data.

下面是读取 4096 个 16 位样本的算法：

ByteArrayOutputStream mainBuffer = new ByteArrayOutputStream();

int minimumBufferSize = AudioRecord.getMinBufferSize(...);

byte[] readBuffer = new byte[minimumBufferSize];

AudioRecord recorder = new AudioRecord(..., minimumBufferSize);

recorder.startRecording();

while (mainBuffer.size() < 8192) {

    // read() is a blocking call
    int bytesRead = recorder.read(readBuffer, 0, minimumBufferSize);

    mainBuffer.write(readBuffer, 0, bytesRead);
}

recorder.stop();

recorder.release();

音频记录缓冲区大小

AudioRecord buffer size

android

audiorecord