Use larger buffer sizes for lower power on Linux.

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 "base/logging.h"
+#include "build/build_config.h"
+
 using base::AutoLock;
 using media::AudioParameters;
 
 namespace media {
 
+#if defined(OS_LINUX)
+#define HIGH_LATENCY_AUDIO_SUPPORT 1
+#endif
+
+#if defined(HIGH_LATENCY_AUDIO_SUPPORT)
+// 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++;
+  return v;
+}
+#endif
+
 AudioHardwareConfig::AudioHardwareConfig(
     const AudioParameters& input_params,
     const AudioParameters& output_params)
     : input_params_(input_params),
-      output_params_(output_params) {
-}
+      output_params_(output_params) {}
 
 AudioHardwareConfig::~AudioHardwareConfig() {}
 
 int AudioHardwareConfig::GetOutputBufferSize() const {
   AutoLock auto_lock(config_lock_);
   return output_params_.frames_per_buffer();
 }
 
 int AudioHardwareConfig::GetOutputSampleRate() const {
   AutoLock auto_lock(config_lock_);
@@ skipping 42 matching lines @@
   AutoLock auto_lock(config_lock_);
   input_params_ = input_params;
 }
 
 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:
+  //
+  //     <= 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);
+  return std::max(output_params_.frames_per_buffer(), high_latency_buffer_size);
+#else
+  return output_params_.frames_per_buffer();
+#endif
+}
+
 }  // namespace media