Substation/LiveCapture.cs

using System.Numerics;
using FftSharp;
using NAudio.CoreAudioApi;
using NAudio.Wave;

namespace Substation;

public class LiveCapture : IDisposable
{
    readonly State _state;
    readonly MMDevice _device;
    WasapiLoopbackCapture? _capture;
    Thread? _processThread;
    volatile bool _running;

    readonly Queue<double> _sampleBuffer = new();
    readonly object _bufferLock = new();

    double[]? _prevRhythmMag;
    double _liveMaxFlux;
    double _liveMaxMelodyEnergy;
    int _sampleRate;
    int _fftsPerTick;
    int _fftIndexInTick;

    public event Action? Stopped;

    public LiveCapture(State state, MMDevice device)
    {
        _state = state;
        _device = device;
    }

    public void Start()
    {
        _running = true;
        _capture = new WasapiLoopbackCapture(_device);
        _sampleRate = _capture.WaveFormat.SampleRate;
        _fftsPerTick = Math.Max(1, (int)Math.Round(MusicAnalyzer.TickDuration * _sampleRate / MusicAnalyzer.HopSize));

        _capture.DataAvailable += OnDataAvailable;
        _capture.RecordingStopped += OnRecordingStopped;

        _processThread = new Thread(ProcessLoop) { IsBackground = true, Name = "LiveCapture-FFT" };
        _processThread.Start();

        _capture.StartRecording();
        Console.WriteLine($"[live] capture started: {_device.FriendlyName} ({_sampleRate}Hz, {_capture.WaveFormat.Channels}ch)");
    }

    public void Stop()
    {
        _running = false;
        try { _capture?.StopRecording(); } catch { }
    }

    void OnDataAvailable(object? sender, WaveInEventArgs e)
    {
        int channels = _capture!.WaveFormat.Channels;
        int bytesPerSample = _capture.WaveFormat.BitsPerSample / 8;
        int frameSize = channels * bytesPerSample;
        int sampleCount = e.BytesRecorded / frameSize;

        lock (_bufferLock)
        {
            for (int i = 0; i < sampleCount; i++)
            {
                int offset = i * frameSize;
                float left = BitConverter.ToSingle(e.Buffer, offset);
                float right = channels >= 2
                    ? BitConverter.ToSingle(e.Buffer, offset + bytesPerSample)
                    : left;
                _sampleBuffer.Enqueue((left + right) * 0.5);
            }

            // Cap buffer size to prevent memory growth if processing falls behind
            while (_sampleBuffer.Count > _sampleRate * 2)
                _sampleBuffer.Dequeue();
        }
    }

    void OnRecordingStopped(object? sender, StoppedEventArgs e)
    {
        _running = false;
        Stopped?.Invoke();
        Console.WriteLine("[live] capture stopped");
    }

    void ProcessLoop()
    {
        var window = new FftSharp.Windows.Hanning();
        var buffer = new double[MusicAnalyzer.WindowSize];
        var tf = new MusicAnalyzer.TickFeature();

        while (_running)
        {
            double[]? windowData = null;

            lock (_bufferLock)
            {
                if (_sampleBuffer.Count >= MusicAnalyzer.WindowSize)
                {
                    for (int i = 0; i < MusicAnalyzer.WindowSize; i++)
                        buffer[i] = _sampleBuffer.Dequeue();
                    windowData = buffer;
                }
            }

            if (windowData == null)
            {
                Thread.Sleep(5);
                continue;
            }

            window.ApplyInPlace(windowData);
            var spectrum = FFT.Forward(windowData);
            var mag = FFT.Magnitude(spectrum);

            var (rhythmEnergy, rhythmFlux, melodyEnergy, melodyFreq) =
                MusicAnalyzer.ExtractFeatures(mag, _prevRhythmMag, _sampleRate);

            _prevRhythmMag = mag;

            // Adaptive normalization: running max with slow decay
            _liveMaxFlux = Math.Max(rhythmFlux, _liveMaxFlux * 0.999);
            _liveMaxMelodyEnergy = Math.Max(melodyEnergy, _liveMaxMelodyEnergy * 0.999);

            tf.RhythmFlux = Math.Max(tf.RhythmFlux, rhythmFlux);
            tf.MelodyEnergy += melodyEnergy;
            tf.MelodyFreqSamples.Add(melodyFreq);
            tf.MelodyCount++;
            _fftIndexInTick++;

            if (_fftIndexInTick >= _fftsPerTick)
            {
                var (frameA, frameB) = MusicAnalyzer.BuildWaveFrame(tf, _liveMaxFlux, _liveMaxMelodyEnergy);
                _state.EnqueueStream('A', new[] { frameA });
                _state.EnqueueStream('B', new[] { frameB });

                tf = new MusicAnalyzer.TickFeature();
                _fftIndexInTick = 0;
            }
        }
    }

    public void Dispose()
    {
        _running = false;
        try { _capture?.Dispose(); } catch { }
    }
}