Add comprehensive diagnostics for process audio capture failures

Addresses issue where Windows 10 Build 19045 users experience inconsistent
process capture support due to audio driver and system configuration variations.

Changes:
- Add Windows version check with user-friendly error messages (Build 19041+ required)
- Implement detailed activation failure diagnostics with specific HRESULT error codes
- Provide actionable guidance for common failures (driver updates, Windows updates, admin rights)
- Add GetActivationResult() method to AudioClientActivationHandler for error retrieval
- Update README with comprehensive explanation of process capture requirements and limitations
- Explain why feature may not work even on correct Windows version (drivers, updates, hardware)
- Document automatic fallback to system-wide audio capture

Users will now see exactly why process capture fails and what they can do to fix it,
with the application gracefully falling back to system-wide capture when needed.

Author: Bri

README.md

@@ -27,7 +27,15 @@ A powerful Windows audio capture application for recording and mixing multiple a
 - **Windows 10 Build 19041+ (Version 2004)** - Required for per-application capture feature
 - No additional software or drivers required
 
-**Note:** On Windows 7/8/8.1 and early Windows 10 builds, only System Audio and Input Devices (microphones) will be available. Per-application capture requires Windows 10 Version 2004 or later.
+**Important Note About Per-Application Capture:**
+
+Per-application capture requires Windows 10 Version 2004 (Build 19041) or later. However, even with the correct Windows version, this feature may not work on all systems due to:
+
+- **Audio driver compatibility** - Some audio drivers don't fully support Windows loopback features
+- **Windows Update level** - Certain KB updates are required for full functionality
+- **Audio device hardware** - Older audio hardware may not support this feature
+
+If per-application capture fails, AudioCapture will automatically fall back to system-wide audio capture and display a detailed error message explaining why. On Windows 7/8/8.1 and early Windows 10 builds, only System Audio and Input Devices (microphones) will be available.
 
 ## How to Use
 

include/AudioCapture.h

@@ -122,6 +122,9 @@ class AudioClientActivationHandler : public IActivateAudioInterfaceCompletionHan
     // Check if the handler is valid (event created successfully)
     bool IsValid() const { return m_completionEvent != nullptr; }
 
+    // Get the activation result (HRESULT code from activation)
+    HRESULT GetActivationResult() const { return m_activationResult; }
+
 private:
     LONG m_refCount;
     HANDLE m_completionEvent;

src/AudioCapture.cpp

@@ -251,6 +251,17 @@ bool AudioCapture::InitializeProcessSpecificCapture(DWORD processId) {
         }
     }
 
+    // Check if Windows version supports process loopback (Build 19041+)
+    if (dwMajorVersion < 10 || (dwMajorVersion == 10 && dwBuild < 19041)) {
+        wchar_t msg[512];
+        swprintf_s(msg, L"Process capture requires Windows 10 Build 19041 or later.\n\n"
+                       L"Your system: Windows %lu Build %lu\n\n"
+                       L"Process capture will not be available. The application will fall back to system-wide audio capture.",
+                       dwMajorVersion, dwBuild);
+        MessageBox(nullptr, msg, L"Process Capture Not Supported", MB_OK | MB_ICONINFORMATION);
+        return false;
+    }
+
     // Use the virtual device for process loopback (not a physical device)
     LPCWSTR deviceId = VIRTUAL_AUDIO_DEVICE_PROCESS_LOOPBACK;
 
@@ -318,15 +329,58 @@ bool AudioCapture::InitializeProcessSpecificCapture(DWORD processId) {
     asyncOp->Release();
 
     if (!success) {
+        // Get the activation result to show detailed error
+        HRESULT activationHr = handler->GetActivationResult();
         handler->Release();
+
+        // Show detailed error message to help user diagnose
+        wchar_t msg[1024];
+        const wchar_t* errorDesc = L"Unknown error";
+
+        // Common error codes and what they mean
+        if (activationHr == E_NOTIMPL || activationHr == 0x88890008) {  // AUDCLNT_E_UNSUPPORTED_FORMAT
+            errorDesc = L"Process loopback audio not supported by your audio driver.\n\n"
+                       L"This is usually caused by:\n"
+                       L"- Outdated or incompatible audio drivers\n"
+                       L"- Missing Windows updates\n"
+                       L"- Audio driver not fully supporting Windows 10 loopback features\n\n"
+                       L"Try updating your audio drivers and Windows.";
+        } else if (activationHr == E_ACCESSDENIED) {
+            errorDesc = L"Access denied to audio device.\n\n"
+                       L"Try running the application as administrator.";
+        } else if (activationHr == 0x887A0002) {  // DXGI_ERROR_NOT_FOUND
+            errorDesc = L"Audio device not found or not available.";
+        } else if (activationHr == 0x88890001) {  // AUDCLNT_E_NOT_INITIALIZED
+            errorDesc = L"Audio client could not be initialized.\n\n"
+                       L"The audio driver may not support this feature.";
+        }
+
+        swprintf_s(msg,
+            L"Process capture failed for this application.\n\n"
+            L"Windows Build: %lu (Requires 19041+)\n"
+            L"Error Code: 0x%08X\n\n"
+            L"%s\n\n"
+            L"The application will fall back to system-wide audio capture.",
+            dwBuild, activationHr, errorDesc);
+
+        MessageBox(nullptr, msg, L"Process Capture Failed", MB_OK | MB_ICONWARNING);
         return false;
     }
 
     // Get the audio client (this AddRefs it for us)
     m_audioClient = handler->GetAudioClient();
 
     if (!m_audioClient) {
+        HRESULT activationHr = handler->GetActivationResult();
         handler->Release();
+
+        wchar_t msg[512];
+        swprintf_s(msg,
+            L"Failed to get audio client for process capture.\n\n"
+            L"Error Code: 0x%08X\n\n"
+            L"The application will fall back to system-wide audio capture.",
+            activationHr);
+        MessageBox(nullptr, msg, L"Process Capture Failed", MB_OK | MB_ICONWARNING);
         return false;
     }