Use examples when they help make things clearer.

In this article, we will discuss the Windows Audio Session API (WASAPI) and how it enables client applications to manage audio data between them and an endpoint device. We’ll also cover some of its interfaces and provide code snippets for reference.

First, what WASAPI is and why we need it in the first place. The Windows Audio Session API (WASAPI) provides a low-latency audio streaming interface that allows applications to manage the flow of audio data between them and an endpoint device. This means that instead of using traditional methods like DirectSound or MME, which can be prone to latency issues and other problems, WASAPI offers a more efficient way to handle audio streams.

To use WASAPI in your application, you’ll need to include the Audioclient.h and Audiopolicy.h header files. These headers define the interfaces that are used by WASAPI to manage audio data. Once you have included these headers, you can create an instance of the IAudioClient interface using the IMMDevice::Activate method with parameter iid set to REFIID IID_IAudioClient.

After initializing a stream on an endpoint device, you can obtain references to other WASAPI interfaces by calling the IAudioClient::GetService method. For example:

“`c++
// Initialize COM library
HRESULT hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);
if (FAILED(hr)) {
printf(“Failed to initialize COM library.\n”);
return 1;
}

// Create device enumerator instance
IMMDeviceEnumerator *pEnumerator = NULL;
hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL, CLSCTX_INPROC_SERVER, __uuidof(IMMDeviceEnumerator), (LPVOID*)&pEnumerator);
if (FAILED(hr)) {
printf(“Failed to create device enumerator instance.\n”);
return 1;
}

// Enumerate audio endpoints
IMMDevice *pDevice = NULL;
hr = pEnumerator->EnumAudioEndpoints(eCapture, DEVICE_STATE_ACTIVE, &GUID_NULL, &pDevice);
if (FAILED(hr)) {
printf(“Failed to enumerate audio endpoints.\n”);
return 1;
}

// Activate audio client interface
IAudioClient *pClient = NULL;
hr = pDevice->Activate(__uuidof(IAudioClient), CLSCTX_INPROC_SERVER, NULL, IID_PPV_ARGS(&pClient));
if (FAILED(hr)) {
printf(“Failed to activate audio client interface.\n”);
return 1;
}

// Get session control interface
IAudioSessionControl *pSession = NULL;
hr = pClient->GetService(__uuidof(IAudioSessionControl), IID_PPV_ARGS(&pSession));
if (FAILED(hr)) {
printf(“Failed to get session control interface.\n”);
return 1;
}

// The following code initializes the COM library, creates a device enumerator instance, enumerates audio endpoints, activates the audio client interface, and gets the session control interface. These steps are necessary for setting up and managing audio streams on an endpoint device.
“`

In this code snippet, we first initialize COM and create an instance of the MMDeviceEnumerator class. We then enumerate all active audio endpoints using the EnumAudioEndpoints method and select one that matches our criteria (in this case, a capture device). Next, we activate the IAudioClient interface on the selected endpoint device and obtain a reference to the IAudioSessionControl interface using the GetService method.

And maybe some examples of when it would be useful to use this API instead of traditional methods like DirectSound or MME?