Use 2 buffers on presumable good Windows boxes.

media/audio/audio_util.cc

Index: media/audio/audio_util.cc
===================================================================
--- media/audio/audio_util.cc	(revision 142383)
+++ media/audio/audio_util.cc	(working copy)
@@ -21,6 +21,7 @@
 #include "base/shared_memory.h"
 #include "base/time.h"
 #if defined(OS_WIN)
+#include "base/sys_info.h"
 #include "base/win/windows_version.h"
 #include "media/audio/audio_manager_base.h"
 #endif
@@ -519,6 +520,20 @@
   return base::win::GetVersion() >= base::win::VERSION_VISTA;
 }
 
+int NumberOfWaveOutBuffers() {
+  // Simple heuristic: use 3 buffers on single-core system or on Vista,
+  // 2 otherwise.
+  // Entire Windows audio stack was rewritten for Windows Vista, and wave out
+  // API is simulated on top of new API, so there is noticeable performance
+  // degradation compared to Windows XP. Part of regression was fixed in
+  // Windows 7. Maybe it is fixed in Vista Serice Pack, but let's be cautious.
+  if ((base::SysInfo::NumberOfProcessors() < 2) ||
+      (base::win::GetVersion() == base::win::VERSION_VISTA)) {
+    return 3;
+  }
+  return 2;
+}
+
 #endif
 
 }  // namespace media