meeting-assistant/MeetingAssistant/Recording/NaudioCaptureSource.cs

using System.Threading.Channels;
using NAudio.CoreAudioApi;
using NAudio.Wave;

namespace MeetingAssistant.Recording;

internal sealed class NaudioCaptureAudioSource : IMeetingAudioSource
{
    private readonly IWaveIn capture;
    private readonly string sourceName;
    private readonly ILogger logger;

    public NaudioCaptureAudioSource(
        IWaveIn capture,
        string sourceName,
        ILogger logger)
    {
        this.capture = capture;
        this.sourceName = sourceName;
        this.logger = logger;
    }

    public IAsyncEnumerable<AudioChunk> CaptureAsync(CancellationToken cancellationToken)
    {
        return CaptureWith(capture, sourceName, logger, cancellationToken);
    }

    private static async IAsyncEnumerable<AudioChunk> CaptureWith(
        IWaveIn capture,
        string sourceName,
        ILogger logger,
        [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
    {
        var channel = Channel.CreateUnbounded<AudioChunk>();
        var chunks = 0;

        capture.DataAvailable += (_, args) =>
        {
            if (args.BytesRecorded <= 0)
            {
                return;
            }

            var buffer = new byte[args.BytesRecorded];
            Buffer.BlockCopy(args.Buffer, 0, buffer, 0, args.BytesRecorded);
            if (Interlocked.Increment(ref chunks) == 1)
            {
                logger.LogInformation(
                    "Audio capture source {SourceName} produced first chunk: {ByteCount} bytes at {SampleRate} Hz/{Channels} channel(s)",
                    sourceName,
                    args.BytesRecorded,
                    capture.WaveFormat.SampleRate,
                    capture.WaveFormat.Channels);
            }

            channel.Writer.TryWrite(new AudioChunk(buffer, capture.WaveFormat.SampleRate, capture.WaveFormat.Channels));
        };
        capture.RecordingStopped += (_, args) =>
        {
            if (args.Exception is not null)
            {
                channel.Writer.TryComplete(args.Exception);
                return;
            }

            channel.Writer.TryComplete();
        };

        try
        {
            using var registration = cancellationToken.Register(capture.StopRecording);
            logger.LogInformation(
                "Starting audio capture source {SourceName} at {SampleRate} Hz/{Channels} channel(s)",
                sourceName,
                capture.WaveFormat.SampleRate,
                capture.WaveFormat.Channels);
            capture.StartRecording();

            await foreach (var chunk in channel.Reader.ReadAllAsync(cancellationToken))
            {
                yield return chunk;
            }
        }
        finally
        {
            capture.Dispose();
        }
    }
}

public sealed class SystemAudioSource : IMeetingAudioSource
{
    private readonly ILogger<SystemAudioSource> logger;

    public SystemAudioSource(ILogger<SystemAudioSource> logger)
    {
        this.logger = logger;
    }

    public IAsyncEnumerable<AudioChunk> CaptureAsync(CancellationToken cancellationToken)
    {
        return CaptureAsync(new MeetingAssistantOptions(), cancellationToken);
    }

    public IAsyncEnumerable<AudioChunk> CaptureAsync(
        MeetingAssistantOptions options,
        CancellationToken cancellationToken)
    {
        var capture = new WasapiLoopbackCapture
        {
            WaveFormat = new WaveFormat(options.Recording.SampleRate, 16, options.Recording.Channels)
        };

        return new NaudioCaptureAudioSource(capture, "system", logger).CaptureAsync(cancellationToken);
    }
}