Enable higher latency audio on Windows for basic playback.

media/base/audio_hardware_config.cc

 // Copyright (c) 2013 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.
 
 #include "media/base/audio_hardware_config.h"
 
 #include <algorithm>
+#include <cmath>
 
 #include "base/logging.h"
 #include "build/build_config.h"
 
 using base::AutoLock;
 using media::AudioParameters;
 
 namespace media {
 
-#if defined(OS_LINUX) || defined(OS_MACOSX)
-#define HIGH_LATENCY_AUDIO_SUPPORT 1
-#endif
-
-#if defined(HIGH_LATENCY_AUDIO_SUPPORT)
+#if !defined(OS_WIN)
 // Taken from "Bit Twiddling Hacks"
 // http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
 static uint32_t RoundUpToPowerOfTwo(uint32_t v) {
   v--;
   v |= v >> 1;
   v |= v >> 2;
   v |= v >> 4;
   v |= v >> 8;
   v |= v >> 16;
   v++;
@@ skipping 63 matching lines @@
 }
 
 void AudioHardwareConfig::UpdateOutputConfig(
     const AudioParameters& output_params) {
   AutoLock auto_lock(config_lock_);
   output_params_ = output_params;
 }
 
 int AudioHardwareConfig::GetHighLatencyBufferSize() const {
   AutoLock auto_lock(config_lock_);
-#if defined(HIGH_LATENCY_AUDIO_SUPPORT)
-  // Empirically, use the nearest higher power of two buffer size corresponding
-  // to 20 ms worth of samples.  For a given sample rate, this works out to:
+
+  // Empirically, we consider 20ms of samples to be high latency.
+  const double twenty_ms_size = 2.0 * output_params_.sample_rate() / 100;
+
+#if defined(OS_WIN)
+  // Windows doesn't use power of two buffer sizes, so we should always round up
+  // to the nearest multiple of the output buffer size.
+  const int high_latency_buffer_size =
+      std::ceil(twenty_ms_size / output_params_.frames_per_buffer()) *
+      output_params_.frames_per_buffer();
+#else
+  // On other platforms use the nearest higher power of two buffer size.  For a
+  // given sample rate, this works out to:
   //
   //     <= 3200   : 64
   //     <= 6400   : 128
   //     <= 12800  : 256
   //     <= 25600  : 512
   //     <= 51200  : 1024
   //     <= 102400 : 2048
   //     <= 204800 : 4096
   //
   // On Linux, the minimum hardware buffer size is 512, so the lower calculated
-  // values are unused.  OSX may have a value as low as 128.  Windows is device
-  // dependent but will generally be sample_rate() / 100.
-  const int high_latency_buffer_size =
-      RoundUpToPowerOfTwo(2 * output_params_.sample_rate() / 100);
+  // values are unused.  OSX may have a value as low as 128.
+  const int high_latency_buffer_size = RoundUpToPowerOfTwo(twenty_ms_size);
+#endif  // defined(OS_WIN)
+
   return std::max(output_params_.frames_per_buffer(), high_latency_buffer_size);
-#else
-  return output_params_.frames_per_buffer();
-#endif
 }
 
 }  // namespace media