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

ViewModels/MainViewModel.cs

@@ -14,6 +14,7 @@ using Microsoft.Win32;
 using ytLive.Helpers;
 using ytLive.Models;
 using ytLive.Services;
+using ytLive.Services.Audio;
 
 namespace ytLive.ViewModels;
 
@@ -79,6 +80,12 @@ public class MainViewModel : ViewModelBase
     private SocialsConfig? _socials;
     private readonly IMicrophoneEnumerator _microphoneEnumerator;
 
+    // Live audio capture (TASK 4 ship step 4): desktop/game via WASAPI loopback,
+    // mic via WASAPI capture, both owned by the mixer and running only while
+    // live. Mic level feeds AudioLevel (the meter); loopback is for the future
+    // encoder mix. Private by design — no UI beyond the existing mic controls.
+    private readonly AudioMixer _audioMixer;
+
     // Screen backdrop: a permanent live capture (desktop/game) that every scene
     // shows at the bottom layer. One shared capture session per key — the
     // ScreenCaptureManager refcounts by key, mirroring CameraManager.
@@ -832,6 +839,12 @@ public class MainViewModel : ViewModelBase
 
         _microphoneEnumerator = new WinRtMicrophoneEnumerator();
 
+        _audioMixer = new AudioMixer(
+            new WasapiMicAudioSource(() => MicSourceName),
+            new WasapiLoopbackAudioSource(),
+            message => AppLog.Write(message));
+        _audioMixer.MicLevelChanged += OnMicLevelChanged;
+
         _fullScreenDetector = new Win32FullScreenDetector();
         foreach (var display in _fullScreenDetector.GetDisplays())
             Displays.Add(display);
@@ -1725,6 +1738,7 @@ public class MainViewModel : ViewModelBase
                 ? "ytLlive"
                 : $"{dialog.StreamTitle} — ytLlive";
             StreamStatus = StreamStatus.Streaming;
+            _audioMixer.Start();
         }
     }
 
@@ -1732,6 +1746,7 @@ public class MainViewModel : ViewModelBase
     {
         StreamStatus = StreamStatus.Offline;
         WindowTitle = "ytLlive";
+        _audioMixer.Stop();
         // Graceful end completes the session = signs out (the DPAPI token is
         // cleared so the next Start Stream requires a fresh sign-in). A crash
         // never runs this, so the token survives and the creator stays signed in.
@@ -1742,6 +1757,17 @@ public class MainViewModel : ViewModelBase
         AppLog.Write("Stream ended; session signed out");
     }
 
+    private void OnMicLevelChanged(float level)
+    {
+        // NAudio raises on its capture thread; marshal to the UI thread so the
+        // meter binding updates safely.
+        var dispatcher = System.Windows.Application.Current?.Dispatcher;
+        if (dispatcher != null && !dispatcher.CheckAccess())
+            dispatcher.BeginInvoke(() => AudioLevel = level);
+        else
+            AudioLevel = level;
+    }
+
     private void UpdateLiveVisuals()
     {
         var live = IsLive;