Desktop Code: AudioCapture Module

This page documents the AudioCapture class used in the Desktop application, which handles input and output audio capture using the Windows Core Audio API (WASAPI)

🧱 Purpose

The AudioCapture module provides low-level access to system audio input and output streams on Windows using the WASAPI interface. This allows capturing real-time audio data from both the microphone and system output (loopback), allowing for the data to be visualized and or used for processing (encoding for recording/streaming).

🔧 Core Responsibilities

• Capture audio from the default input device (microphone).
• Capture audio from the default output device (system loopback).
• Extract volume levels in decibels (dB) from both input and output.
• Proper resource management and COM lifecycle handling.
• Thread-safe start/stop for capture.

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🛠️ Key Methods

Constructor

AudioCapture::AudioCapture();

• Initializes the COM library and sets up the device enumerator for audio device management.

Destructor

AudioCapture::~AudioCapture();

Stops any ongoing capture, releases resources and uninitializes COM.

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🔌 Device Setup

Initialize Input Device

bool AudioCapture::initializeInput();

• Activates the default microphone
• Prepares an event-driven audio client
• Retrieves the mix format and capture client

Initialize Output Device (Loopback)

bool AudioCapture::initializeOutput();

• Activates the default output device (speakers)
• Initializes in loopback mode for capturing output audio.
• Retrieve mix format and capture client.

▶️ Control

Start Capturing

void AudioCapture::startCapture();

Stars capturing from the initialized devices (if available).

Stop Capturing

void AudioCapture::stopCapture();

Stops the audio stream and resets capture flags.

📊 Volume Extraction

Get output volume

float AudioCapture::getOutputVolume();

• Returns volume in dB (float) from the output stream.
• uses RMS (Root Mean Square) calculation.

Get input volume

float AudioCapture::getInputVolume();

• Returns volume in dB (float) from the microphone stream.
• Uses the same RMS volume calculation method.

📐 Volume Calculations

float calculateRMSVolume(BYTE* pData, UINT32 numFrames, WAVEFORMATEX* pwfx);
float convertToDecibels(float rmsVolume);

These convert raw PCM data into a normalized volume level, and then to decibels.

🛑 Error Handling

All errors are logged using qDebug() from the Qt framework. Make sure

🧪 Example Usage

AudioCapture audio;
audio.initializeInput();
audio.initializeOutput();
audio.startCapture();

float micVolume = audio.getInputVolume();
float sysVolume = audio.getOutputVolume();

audio.stopCapture();

📂 Related files

• AudioCapture.h
• AudioCapture.cpp

🧱 Dependencies

• Qt (for qDebug())
• Windows Core Audio APIs (WASAPI)