TASK 4 ship step 4: WASAPI audio capture — NAudio loopback + mic behind an IAudioSource seam, AudioMixer driving AudioLevel while live, pure level meter + WaveToFloat, NAudio.Wasapi 2.2.1 (MIT, notices item 9) — 139 tests passing, 0 warnings

Services/Audio/AudioLevelMeter.cs

@@ -0,0 +1,35 @@
+namespace ytLive.Services.Audio;
+
+/// <summary>
+/// Computes the smoothed mic level (0..1) from captured samples. Pure —
+/// unit-tested; the <see cref="AudioMixer"/> only feeds it and forwards the
+/// result. RMS-based so it tracks perceived loudness, smoothed so the meter
+/// does not flicker.
+/// </summary>
+public sealed class AudioLevelMeter
+{
+    private const float Smoothing = 0.2f;
+    private float _level;
+
+    public float Level => _level;
+
+    public float Push(AudioSample sample)
+    {
+        if (sample.Samples.Length == 0)
+            return _level;
+
+        double sumSquares = 0;
+        var count = 0;
+        foreach (var value in sample.Samples)
+        {
+            sumSquares += value * value;
+            count++;
+        }
+
+        var rms = (float)Math.Sqrt(sumSquares / count);
+        _level = _level * (1 - Smoothing) + rms * Smoothing;
+        return _level;
+    }
+
+    public void Reset() => _level = 0;
+}