Low-latency AudioOutputStream implementation based on WASAPI for Windows.

media/audio/audio_util.cc

 // Copyright (c) 2011 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.
 
 #include <algorithm>
 
 #include "base/atomicops.h"
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/shared_memory.h"
 #if defined(OS_WIN)
 #include "base/win/windows_version.h"
 #endif
 #include "media/audio/audio_util.h"
 #if defined(OS_MACOSX)
 #include "media/audio/mac/audio_low_latency_input_mac.h"
 #include "media/audio/mac/audio_low_latency_output_mac.h"
 #endif
 #if defined(OS_WIN)
 #include "media/audio/win/audio_low_latency_input_win.h"
+#include "media/audio/win/audio_low_latency_output_win.h"
 #endif
 
 using base::subtle::Atomic32;
 
 const uint32 kUnknownDataSize = static_cast<uint32>(-1);
 
 namespace media {
 
 // TODO(fbarchard): Convert to intrinsics for better efficiency.
 template<class Fixed>
@@ skipping 197 matching lines @@
 
       destination[j * channels + i] = static_cast<int16>(sample);
     }
   }
 }
 
 double GetAudioHardwareSampleRate() {
 #if defined(OS_MACOSX)
     // Hardware sample-rate on the Mac can be configured, so we must query.
     return AUAudioOutputStream::HardwareSampleRate();
+#elif defined(OS_WIN)
+  if (base::win::GetVersion() <= base::win::VERSION_XP) {
+    // Fall back to Windows Wave implementation on Windows XP or lower
+    // and use 48kHz as default input sample rate.
+    return 48000.0;
+  } else {

[scherkus (not reviewing), 2011/11/08 23:52:21]

nit: no need for else statement if you return

[henrika (OOO until Aug 14), 2011/11/09 13:59:22]

Done.

+    // Hardware sample-rate on Windows can be configured, so we must query.
+    // TODO(henrika): improve possibility to specify audio endpoint.
+    // Use the default device (same as for Wave) for now to be compatible.
+    return WASAPIAudioOutputStream::HardwareSampleRate(eConsole);
+  }
 #else
-    // Hardware for Windows and Linux is nearly always 48KHz.
+    // Hardware for Linux is nearly always 48KHz.
     // TODO(crogers) : return correct value in rare non-48KHz cases.
     return 48000.0;
 #endif
 }
 
 double GetAudioInputHardwareSampleRate() {
 #if defined(OS_MACOSX)
   // Hardware sample-rate on the Mac can be configured, so we must query.
   return AUAudioInputStream::HardwareSampleRate();
 #elif defined(OS_WIN)
@@ skipping 12 matching lines @@
   // TODO(henrika): return correct value in rare non-48KHz cases.
   return 48000.0;
 #endif
 }
 
 size_t GetAudioHardwareBufferSize() {
   // The sizes here were determined by experimentation and are roughly
   // the lowest value (for low latency) that still allowed glitch-free
   // audio under high loads.
   //
-  // For Mac OS X the chromium audio backend uses a low-latency
-  // CoreAudio API, so a low buffer size is possible.  For other OSes,
-  // further tuning may be needed.
+  // For Mac OS X and Windows the chromium audio backend uses a low-latency
+  // Core Audio API, so a low buffer size is possible. For Linux, further
+  // tuning may be needed.
+  // TODO(crogers): figure out the best possible buffer sizes for WebAudio.
 #if defined(OS_MACOSX)
   return 128;
-#elif defined(OS_LINUX)
-  return 2048;
+#elif defined(OS_WIN)
+  int mixing_sample_rate =
+      static_cast<int>(WASAPIAudioOutputStream::HardwareSampleRate(eConsole));
+  if (mixing_sample_rate == 48000 || mixing_sample_rate == 44100)
+    return 1024;
+  else if (mixing_sample_rate == 96000)

[scherkus (not reviewing), 2011/11/08 23:52:21]

ditto

[henrika (OOO until Aug 14), 2011/11/09 13:59:22]

Done.

+    return 2048;
+  else
+    return 2048;
 #else
   return 2048;
 #endif
 }
 
 // When transferring data in the shared memory, first word is size of data
 // in bytes. Actual data starts immediately after it.
 
 uint32 TotalSharedMemorySizeInBytes(uint32 packet_size) {
   // Need to reserve extra 4 bytes for size of data.
@@ skipping 36 matching lines @@
   char* ptr = static_cast<char*>(shared_memory->memory()) + shared_memory_size;
   DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3);
 
   // Actual data size stored at the end of the buffer.
   uint32 actual_data_size =
       base::subtle::Acquire_Load(reinterpret_cast<volatile Atomic32*>(ptr));
   return actual_data_size == kUnknownDataSize;
 }
 
 }  // namespace media