WASAPI:以最小的延迟播放正弦波声音，无毛刺(专用事件驱动模式）

WASAPI: Play sine wave sound in minimum latency without glitches (exclusive-event driven mode)

本文关键字：毛刺 专用 模式 事件驱动 声音 正弦波 播放 延迟 WASAPI      更新时间：2023-10-16

我正在尝试在独占模式下使用 Windows 音频会话 API （WASAPI） 播放简单的正弦波形，但无论我做什么都会遇到声音故障。我一直在使用 MSDN 独占模式流示例作为参考点，下面是稍微调整的代码当前的样子。

设置代码：

-- <variable declarations, incl. "HRESULT hr; BYTE *pData;" > --
// also, hr is checked for errors every step of the way
hr = CoCreateInstance(
    CLSID_MMDeviceEnumerator, NULL,
    CLSCTX_ALL, IID_IMMDeviceEnumerator,
    (void**)&pEnumerator);
hr = pEnumerator->GetDefaultAudioEndpoint(
    eRender, eConsole, &pDevice);
hr = pDevice->Activate(
    IID_IAudioClient, CLSCTX_ALL,
    NULL, (void**)&pAudioClient);

REFERENCE_TIME DefaultDevicePeriod = 0, MinimumDevicePeriod = 0;
hr = pAudioClient->GetDevicePeriod(&DefaultDevicePeriod, &MinimumDevicePeriod);
WAVEFORMATEX wave_format = {};
wave_format.wFormatTag = WAVE_FORMAT_PCM;
wave_format.nChannels = 2;
wave_format.nSamplesPerSec = 44100;
wave_format.nAvgBytesPerSec = 44100 * 2 * 16 / 8;
wave_format.nBlockAlign = 2 * 16 / 8;
wave_format.wBitsPerSample = 16;
hr = pAudioClient->IsFormatSupported(
    AUDCLNT_SHAREMODE_EXCLUSIVE,
    &wave_format,
    NULL // can't suggest a "closest match" in exclusive mode
    );
hr = pAudioClient->Initialize(
    AUDCLNT_SHAREMODE_EXCLUSIVE,
    AUDCLNT_STREAMFLAGS_EVENTCALLBACK,
    MinimumDevicePeriod,
    MinimumDevicePeriod,
    &wave_format,
    NULL);

// Get the actual size of the allocated buffer.
hr = pAudioClient->GetBufferSize(&bufferFrameCount);
INT32 FrameSize_bytes = bufferFrameCount * wave_format.nChannels * wave_format.wBitsPerSample / 8;
hr = pAudioClient->GetService(
    IID_IAudioRenderClient,
    (void**)&pRenderClient);
hEvent = CreateEvent(nullptr, false, false, nullptr);
if (hEvent == INVALID_HANDLE_VALUE) { printf("CreateEvent failedn");  return -1; }
hr = pAudioClient->SetEventHandle(hEvent);

缓冲区设置：

const size_t num_samples = FrameSize_bytes / sizeof(unsigned short);
unsigned short *samples = new unsigned short[num_samples];
float min = (float)(std::numeric_limits<unsigned short>::min)();
float max = (float)(std::numeric_limits<unsigned short>::max)();
float halfmax = max / 2.0;
float dt = 1.0 / (float)wave_format.nSamplesPerSec;
float freq = (float)wave_format.nSamplesPerSec / (float)bufferFrameCount;
for (int i = 0; i < num_samples/2; ++i) {
    float t = (float)i * dt;
    samples[2*i] = sin_minmax_Hz(min, max, freq, t);
    samples[2*i + 1] = sin_minmax_Hz(min, max, freq, t);
}
hr = pRenderClient->GetBuffer(bufferFrameCount, &pData);
memcpy(pData, samples, FrameSize_bytes);
hr = pRenderClient->ReleaseBuffer(bufferFrameCount, flags);
DWORD taskIndex = 0;
hTask = AvSetMmThreadCharacteristics(TEXT("Pro Audio"), &taskIndex);
if (hTask == NULL) {
    hr = E_FAIL;
    IF_ERROR_EXIT(hr);
}

函数sin_minmax_Hz定义如下：

#define TWO_PI (3.14159265359*2)
static inline float sin01(float alpha) {
    return 0.5*sin(alpha) + 0.5;
}
static inline float sin_minmax_Hz(float min, float max, float freq_Hz, float t) {
    return (max - min) / 2.0 * sin01(t * freq_Hz * TWO_PI);
}

回放：

hr = pAudioClient->Start();  // Start playing.
IF_ERROR_EXIT(hr);
// just play indefinitely
while (true) {
    WaitForSingleObject(hEvent, INFINITE);
    hr = pRenderClient->GetBuffer(bufferFrameCount, &pData);
    memcpy(pData, samples, FrameSize_bytes);
    hr = pRenderClient->ReleaseBuffer(bufferFrameCount, 0);
}

问题在于，在最小延迟下，正弦波通常会流畅地播放大约 2 秒，然后开始出现大量混叠的毛刺，听起来几乎像锯齿波。我在这里错过了什么吗？

（完整的工作示例可以在这里找到。

刚刚尝试了完整的示例，IAudioClient：：Initialize 失败并显示AUDCLNT_E_BUFFER_SIZE_NOT_ALIGNED。此错误是在 Windows 7 中引入的，您运行的是 vista 吗？在校正对齐的周期大小后，我得到了一个完美的正弦波。如果系统未生成此错误，请尝试在 128 字节（非位）边界上手动对齐缓冲区。否则，这是对齐代码：

hr = pAudioClient->Initialize(
        AUDCLNT_SHAREMODE_EXCLUSIVE,
        AUDCLNT_STREAMFLAGS_EVENTCALLBACK,
        MinimumDevicePeriod,
        MinimumDevicePeriod,
        &wave_format,
        NULL);
  if(hr == AUDCLNT_E_BUFFER_SIZE_NOT_ALIGNED) {
    UINT32 nFramesInBuffer;
    REFERENCE_TIME hnsPeriod;
    hr = pAudioClient->GetBufferSize(&nFramesInBuffer);
    IF_ERROR_EXIT(hr);
    hnsPeriod = (REFERENCE_TIME)(REFTIMES_PER_SEC * nFramesInBuffer / wave_format.nSamplesPerSec + 0.5);
    hr = pAudioClient->Release();
    IF_ERROR_EXIT(hr);
    hr = pDevice->Activate(__uuidof(IAudioClient), CLSCTX_ALL, NULL, (void**)&pAudioClient);
    IF_ERROR_EXIT(hr);
    hr = pAudioClient->Initialize(AUDCLNT_SHAREMODE_EXCLUSIVE, AUDCLNT_STREAMFLAGS_EVENTCALLBACK, hnsPeriod, hnsPeriod, &wave_format, NULL);
    IF_ERROR_EXIT(hr);
  }

我遇到了同样的问题。尝试在命令Start()之前插入pAudioClient->Reset()。喜欢这个：

hr = pAudioClient->Reset();
if (hr) .....
hr = pAudioClient->Start();

它对我有用。祝你好运。

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