Audio Capture and System Sound Recording in C# .NET¶

Introduction¶

The VisioForge Video Capture SDK provides audio capture capabilities for .NET developers, covering microphone recording, system audio (loopback/speaker) capture, and combined audio recording. Whether you're building a podcast recorder, screen recording tool with audio, or a voice capture application, the SDK handles device enumeration, format negotiation, and encoding.

This guide provides complete, runnable code examples for the most common audio capture scenarios using both the Video Capture SDK X and Media Blocks SDK APIs.

Supported Audio Sources¶

Physical microphones — Desktop, USB, and Bluetooth microphones
Line-in ports — External mixers or instruments
System audio (loopback) — Record what's playing through your speakers or headphones
Virtual audio devices — Capture audio from other applications
Network streams — Audio from RTSP, HTTP, and other streaming sources

For detailed source configuration, see Audio Sources.

Audio Format Support¶

Lossy Formats¶

MP3 — Industry standard, adjustable bitrates from 8 kbps to 320 kbps
M4A (AAC) — Excellent quality-to-size ratio
Windows Media Audio — Good compression with Windows integration
Ogg Vorbis — Open-source, excellent quality at lower bitrates
Speex — Optimized for speech

Lossless Formats¶

WAV — Uncompressed, perfect quality
FLAC — Lossless compression without quality loss

Record Microphone Audio to MP3¶

This console application records audio from the default microphone and saves it as an MP3 file.

Required NuGet Packages¶

dotnet add package VisioForge.DotNet.Core.TRIAL
dotnet add package VisioForge.DotNet.VideoCapture.TRIAL

Add the redist package for your platform (e.g., VisioForge.DotNet.Redist.Base.Windows.x64).

Complete Example¶

using System;
using System.IO;
using System.Threading.Tasks;
using VisioForge.Core;
using VisioForge.Core.Types.X.Output;
using VisioForge.Core.Types.X.Sources;
using VisioForge.Core.VideoCaptureX;

class Program
{
    static async Task Main(string[] args)
    {
        // Initialize SDK
        await VisioForgeX.InitSDKAsync();

        var videoCapture = new VideoCaptureCoreX();

        try
        {
            // Enumerate audio capture devices
            var audioDevices = await DeviceEnumerator.Shared.AudioSourcesAsync(
                AudioCaptureDeviceAPI.DirectSound);

            if (audioDevices.Length == 0)
            {
                Console.WriteLine("No audio capture device found.");
                return;
            }

            // Display available devices
            Console.WriteLine("Available audio devices:");
            for (int i = 0; i < audioDevices.Length; i++)
            {
                Console.WriteLine($"  {i + 1}. {audioDevices[i].DisplayName}");
            }

            // Select first device (default microphone)
            var selectedDevice = audioDevices[0];
            var audioFormat = selectedDevice.GetDefaultFormat();
            var audioSource = selectedDevice.CreateSourceSettingsVC(audioFormat);

            // Configure audio-only capture
            videoCapture.Audio_Source = audioSource;
            videoCapture.Video_Source = null;
            videoCapture.Video_Play = false;
            videoCapture.Audio_Play = false;
            videoCapture.Audio_Record = true;

            // Configure MP3 output
            string outputPath = Path.Combine(
                Environment.GetFolderPath(Environment.SpecialFolder.MyMusic),
                $"mic_recording_{DateTime.Now:yyyyMMdd_HHmmss}.mp3");

            var mp3Output = new MP3Output(outputPath);
            videoCapture.Outputs_Add(mp3Output, autostart: true);

            // Start recording
            await videoCapture.StartAsync();
            Console.WriteLine($"Recording to: {outputPath}");
            Console.WriteLine("Press ENTER to stop...");
            Console.ReadLine();

            // Stop and save
            await videoCapture.StopAsync();
            Console.WriteLine("Recording saved.");
        }
        finally
        {
            await videoCapture.DisposeAsync();
            VisioForgeX.DestroySDK();
        }
    }
}

Capture System Audio (Speaker / Loopback)¶

System audio capture (also called loopback or speaker capture) records any sound playing through your computer's output device. This is commonly used for screen recording with audio, capturing conference calls, or recording streaming audio.

On Windows, loopback capture uses the WASAPI2 API to access output devices.

Complete Example — Video Capture SDK X¶

using System;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using VisioForge.Core;
using VisioForge.Core.Types.X.Output;
using VisioForge.Core.Types.X.Sources;
using VisioForge.Core.VideoCaptureX;

class Program
{
    static async Task Main(string[] args)
    {
        // Initialize SDK
        await VisioForgeX.InitSDKAsync();

        var videoCapture = new VideoCaptureCoreX();

        try
        {
            // Enumerate WASAPI2 audio output devices (speakers/headphones)
            var audioOutputs = await DeviceEnumerator.Shared.AudioOutputsAsync(
                AudioOutputDeviceAPI.WASAPI2);

            if (audioOutputs.Length == 0)
            {
                Console.WriteLine("No WASAPI2 audio output device found.");
                return;
            }

            // Display available loopback sources
            Console.WriteLine("Available loopback devices:");
            for (int i = 0; i < audioOutputs.Length; i++)
            {
                Console.WriteLine($"  {i + 1}. {audioOutputs[i].Name}");
            }

            // Select the first device
            var outputDevice = audioOutputs[0];

            // Create loopback source settings
            var audioSource = new LoopbackAudioCaptureDeviceSourceSettings(outputDevice);
            videoCapture.Audio_Source = audioSource;

            // Configure for audio-only capture
            videoCapture.Audio_Play = false;
            videoCapture.Audio_Record = true;
            videoCapture.Video_Play = false;

            // Configure M4A (AAC) output
            string outputPath = Path.Combine(
                Environment.GetFolderPath(Environment.SpecialFolder.MyMusic),
                $"system_audio_{DateTime.Now:yyyyMMdd_HHmmss}.m4a");

            var m4aOutput = new M4AOutput(outputPath);
            videoCapture.Outputs_Add(m4aOutput, autostart: true);

            // Start capturing system audio
            await videoCapture.StartAsync();
            Console.WriteLine($"Capturing system audio to: {outputPath}");
            Console.WriteLine("Play some audio on your computer, then press ENTER to stop...");
            Console.ReadLine();

            // Stop and save
            await videoCapture.StopAsync();
            Console.WriteLine("Recording saved.");
        }
        finally
        {
            await videoCapture.DisposeAsync();
            VisioForgeX.DestroySDK();
        }
    }
}

Complete Example — Media Blocks SDK¶

The Media Blocks SDK uses a pipeline approach where you connect source, processing, and output blocks. This example captures system audio using SystemAudioSourceBlock and saves it to an M4A file.

using System;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using VisioForge.Core;
using VisioForge.Core.MediaBlocks;
using VisioForge.Core.MediaBlocks.Sources;
using VisioForge.Core.MediaBlocks.Sinks;
using VisioForge.Core.Types.X.Sources;

class Program
{
    static async Task Main(string[] args)
    {
        // Initialize SDK
        await VisioForgeX.InitSDKAsync();

        MediaBlocksPipeline pipeline = null;

        try
        {
            // Get the first WASAPI2 output device for loopback capture
            var audioOutputs = await DeviceEnumerator.Shared.AudioOutputsAsync(
                AudioOutputDeviceAPI.WASAPI2);

            if (audioOutputs.Length == 0)
            {
                Console.WriteLine("No WASAPI2 audio output device found.");
                return;
            }

            var outputDevice = audioOutputs[0];
            Console.WriteLine($"Using loopback device: {outputDevice.Name}");

            // Create pipeline
            pipeline = new MediaBlocksPipeline();

            // Create loopback audio source
            var sourceSettings = new LoopbackAudioCaptureDeviceSourceSettings(outputDevice);
            var audioSource = new SystemAudioSourceBlock(sourceSettings);

            // Create M4A output
            string outputPath = Path.Combine(
                Environment.GetFolderPath(Environment.SpecialFolder.MyMusic),
                $"system_audio_{DateTime.Now:yyyyMMdd_HHmmss}.m4a");

            var output = new M4AOutputBlock(outputPath);

            // Connect source to output
            pipeline.Connect(audioSource, output);

            // Start pipeline
            await pipeline.StartAsync();
            Console.WriteLine($"Capturing system audio to: {outputPath}");
            Console.WriteLine("Press ENTER to stop...");
            Console.ReadLine();

            // Stop pipeline
            await pipeline.StopAsync();
            Console.WriteLine("Recording saved.");
        }
        finally
        {
            if (pipeline != null)
            {
                await pipeline.DisposeAsync();
            }

            VisioForgeX.DestroySDK();
        }
    }
}

Key Features¶

Device Control¶

Enumerate all available audio input and output devices
Select specific input devices programmatically
Set input volume levels and mute status
Monitor audio levels in real-time with VU meters
Auto-select default system devices

Advanced Processing¶

Real-time audio visualization with spectrum and waveform analysis
Noise reduction and echo cancellation
Gain control and normalization
Voice activity detection (VAD)
Stereo/mono channel management
Sample rate conversion

Recording Controls¶

Start, pause, resume, and stop recording
Buffer management for low-latency operation
Timed recordings with automatic stop
File splitting for large recordings
Auto file naming with timestamps

Cross-Platform Notes¶

Platform	Microphone	System Audio (Loopback)
Windows	DirectSound, WASAPI2	WASAPI2 loopback
macOS	CoreAudio	Not available via SDK
Linux	PulseAudio, ALSA	PulseAudio monitor

System audio loopback capture is primarily a Windows feature using the WASAPI2 API. On Linux, PulseAudio monitor devices may provide similar functionality.

Best Practices¶

Check device availability before starting capture — devices can be disconnected at any time
Monitor audio levels during recording to detect silence or clipping
Choose the right format — MP3/M4A for compressed output, WAV for maximum quality, FLAC for lossless compression
Use WASAPI2 for loopback capture on Windows — it provides the lowest latency and most reliable system audio capture
Handle errors gracefully — implement error handling for device disconnection events
Test on target hardware — audio device behavior varies across systems

Sample Applications¶

Complete working examples are available on GitHub: