android - 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:

• 我必须从缓冲区中读取短裤，因为我指定了 ENCODING_PCM_16BIT。是否正确？
• 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 实例将接受的最小大小。这就像一个阈值。 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();