After spending some time working with C#, I hit a pretty big wall when trying to play audio on a specific audio device in my AvaloniaUI project. I ended up getting it working after combining a few different solutions, so I decided to put the solution here in case anyone else needs it!

The Problem

All the code I could find to get a list of all active audio output devices required use of the MMDeviceEnumerator class. The problem is that in order to play sound on a specific device, NAudio recommends using the WaveOut class, where you can specify the DeviceNumber property. Unfortunately, MMDeviceEnumerator and WaveOut list the devices in a different order. I couldn't just use the WaveOut class because it limits the name of the audio devices to 31 characters, and I wanted to show the full name.

The First Issue: WaveOut does not exist in current context

The first issue I ran into was that I couldn't use the WaveOut class. All the code samples I found used it, but I couldn't find it in the NAudio library.

After some digging, I found that the I had to add the NAudio.WinForms package to my project. This added the WaveOut class to the NAudio namespace.

Adding the Nuget package

1. Right-click your project in the Solution Explorer
2. Click "Manage Nuget Packages"
3. Search for "NAudio.WinForms"
4. Click "Install"

The Solution

using Avalonia.Soundboard.Models;
using NAudio.CoreAudioApi;
using NAudio.Wave;
using ReactiveUI;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Avalonia.Soundboard.ViewModels
{
    public class MainWindowViewModel : ViewModelBase, IDisposable
    {
        private readonly MMDeviceEnumerator _enumerator;
        private readonly List<AudioDevice> _audioDevices;
        private AudioDevice? _selectedAudioDevice;

        public MainWindowViewModel()
        {
            _enumerator = new();
            _audioDevices = new();

            LoadAudioDevices();
        }

        private void LoadAudioDevices()
        {
            // Select all active audio devices
            // We use the MMDeviceEnumerator to get the audio device full names since WaveOut limits device names to 31 characters.
            // However, we use the WaveOut device order to determine the device number, since the order is different between the two.

            foreach (var mmDevice in _enumerator.EnumerateAudioEndPoints(DataFlow.Render, DeviceState.Active))
            {
                // Only keep active devices
                if (mmDevice.State != DeviceState.Active)
                {
                    continue;
                }

                // Find the matching WaveOut device for the MMDevice
                for (var deviceNumber = -1; deviceNumber < WaveOut.DeviceCount; deviceNumber++)
                {
                    if (mmDevice.FriendlyName.StartsWith(WaveOut.GetCapabilities(deviceNumber).ProductName))
                    {
                        _audioDevices.Add(new AudioDevice(mmDevice, deviceNumber));
                        break;
                    }
                }
            }

            // If no audio devices
            if (_audioDevices.Count == 0)
            {
                throw new Exception("No audio devices found");
            }
            // TODO - Load this from settings
            _selectedAudioDevice = _audioDevices[0];
        }

        public void PlaySound(string path)
        {
            var reader = new Mp3FileReader(path);
            WaveOutEvent waveOut = new()
            {
                DeviceNumber = _selectedAudioDevice.DeviceNumber
            };
            waveOut.Init(reader);
            waveOut.Play();
        }

        public void Dispose()
        {
            _enumerator.Dispose();
            GC.SuppressFinalize(this);
        }

        public string[] AudioDevices
            => _audioDevices.Select(x => x.Device.FriendlyName).ToArray();

        public string SelectedAudioDevice
        {
            get => _selectedAudioDevice.Device.FriendlyName;
            set => this.RaiseAndSetIfChanged(ref _selectedAudioDevice, _audioDevices.Find(x => x.Device.FriendlyName == value));
        }

    }
}

Conclusion

I hope this helps someone else out there! I spent a lot of time trying to figure this out, and I'm glad I finally got it working.