Substation/LiveCapture.cs

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 _liveMaxMelodyEnergy;
    int _sampleRate;
    int _fftsPerTick;
    int _fftIndexInTick;
    readonly DrumDetector _drums = new();

    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();
        double[]? overlap = null; // last HopSize samples from previous window

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

            lock (_bufferLock)
            {
                int needed = overlap != null ? MusicAnalyzer.HopSize : MusicAnalyzer.WindowSize;
                if (_sampleBuffer.Count >= needed)
                {
                    if (overlap != null)
                    {
                        Array.Copy(overlap, 0, buffer, 0, MusicAnalyzer.HopSize);
                        for (int i = 0; i < MusicAnalyzer.HopSize; i++)
                            buffer[MusicAnalyzer.HopSize + i] = _sampleBuffer.Dequeue();
                    }
                    else
                    {
                        for (int i = 0; i < MusicAnalyzer.WindowSize; i++)
                            buffer[i] = _sampleBuffer.Dequeue();
                    }
                    // Save last HopSize samples for next window's overlap
                    overlap = new double[MusicAnalyzer.HopSize];
                    Array.Copy(buffer, MusicAnalyzer.HopSize, overlap, 0, MusicAnalyzer.HopSize);
                    windowData = buffer;
                }
            }

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

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

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

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

            // Drum detection: map this FFT window to a sub-tick (0-3)
            int subTick = _fftsPerTick > 0 ? _fftIndexInTick * 4 / _fftsPerTick : 0;
            if (subTick > 3) subTick = 3;
            _drums.ProcessWindow(mag, _sampleRate, MusicAnalyzer.WindowSize, subTick);

            // Melody accumulation for chB
            tf.MelodyEnergy += melodyEnergy;
            tf.MelodyFreqSamples.Add(melodyFreq);
            tf.MelodyCount++;
            _fftIndexInTick++;

            if (_fftIndexInTick >= _fftsPerTick)
            {
                var frameA = _drums.BuildFrame();
                var frameB = MusicAnalyzer.BuildMelodyFrame(tf, _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 { }
    }
}