Increase the number of wave out buffers to 4 for Vista.

media/audio/audio_util.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Software adjust volume of samples, allows each audio stream its own
 // volume without impacting master volume for chrome and other applications.
 
 // Implemented as templates to allow 8, 16 and 32 bit implementations.
 // 8 bit is unsigned and biased by 128.
 
@@ skipping 524 matching lines @@
 
 #if defined(OS_WIN)
 
 bool IsWASAPISupported() {
   // Note: that function correctly returns that Windows Server 2003 does not
   // support WASAPI.
   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 apparently fixed
-  // in Windows 7, but problems remain at least with some configurations.
-  if ((base::SysInfo::NumberOfProcessors() < 2) ||
-      (base::win::GetVersion() >= base::win::VERSION_VISTA)) {
+  // The entire Windows audio stack was rewritten for Windows Vista, and the
+  // wave out API is simulated on top of new API, so there is noticeable
+  // performance degradation compared to Windows XP. So use 4 buffers for Vista.
+  if (base::win::GetVersion() == base::win::VERSION_VISTA)
+    return 4;
+
+  // Part of regression was apparently fixed in Windows 7, but problems remain
+  // at least with some configurations (compared to XP). So use 3 buffers for
+  // Windows 7 and higher.
+  if (base::win::GetVersion() >= base::win::VERSION_WIN7)
     return 3;
-  }
-  return 2;
+
+  // Otherwise (for XP), use 3 buffers on single-core systems and 2 otherwise.
+  return (base::SysInfo::NumberOfProcessors() < 2) ? 3 : 2;
 }
 
 #endif
 
 }  // namespace media