Windows Audio Session API (WASAPI) is a Microsoft API that provides low-latency, high-quality audio streaming capabilities on Windows platforms. It is a part of the Core Audio APIs introduced in Windows Vista and is used extensively in professional audio applications for tasks such as audio capture and playback.

WASAPI operates in two modes: exclusive and shared. Exclusive mode allows an application to take complete control over an audio endpoint, while shared mode allows multiple applications to share the audio endpoint. This article will guide you through setting up and using WASAPI for audio tasks in a Windows environment.

Examples:

1. Setting Up a WASAPI Audio Capture Application

   To capture audio using WASAPI, you need to follow these basic steps:

   • Initialize the COM library.
   • Obtain an audio endpoint.
   • Activate the endpoint for capture.
   • Configure the audio client.
   • Start capturing audio.

   Here is a simplified example using C++:

   #include <iostream>
   #include <mmdeviceapi.h>
   #include <audioclient.h>
   
   int main() {
      CoInitialize(NULL);
   
      // Get the default audio endpoint
      IMMDeviceEnumerator *deviceEnumerator = NULL;
      CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&deviceEnumerator));
   
      IMMDevice *defaultDevice = NULL;
      deviceEnumerator->GetDefaultAudioEndpoint(eCapture, eConsole, &defaultDevice);
   
      // Activate the audio client
      IAudioClient *audioClient = NULL;
      defaultDevice->Activate(__uuidof(IAudioClient), CLSCTX_INPROC_SERVER, NULL, (void**)&audioClient);
   
      // Initialize the audio client
      WAVEFORMATEX *waveFormat;
      audioClient->GetMixFormat(&waveFormat);
      audioClient->Initialize(AUDCLNT_SHAREMODE_SHARED, 0, 0, 0, waveFormat, NULL);
   
      // Start capturing
      IAudioCaptureClient *captureClient;
      audioClient->GetService(__uuidof(IAudioCaptureClient), (void**)&captureClient);
      audioClient->Start();
   
      // Capture loop (simplified)
      BYTE *data;
      UINT32 packetLength = 0;
      while (true) {
          captureClient->GetNextPacketSize(&packetLength);
          if (packetLength > 0) {
              captureClient->GetBuffer(&data, &packetLength, NULL, NULL, NULL);
              // Process audio data here
              captureClient->ReleaseBuffer(packetLength);
          }
      }
   
      // Cleanup
      audioClient->Stop();
      CoUninitialize();
      return 0;
   }

   This example initializes the COM library, retrieves the default audio capture device, and starts capturing audio data.

2. Using WASAPI in Exclusive Mode for Low-Latency Audio Playback

   Exclusive mode is used when low-latency audio is required. Here’s a basic example of setting up WASAPI for playback in exclusive mode:

   // Similar setup as above, but with exclusive mode initialization
   audioClient->Initialize(AUDCLNT_SHAREMODE_EXCLUSIVE, 0, 10000000, 0, waveFormat, NULL);

   In exclusive mode, you must manage the audio buffer size and timing precisely to prevent glitches.