Clean up audio-related utility functions to compute buffer sizes

content/renderer/media/audio_hardware.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.
 
 #include "content/renderer/media/audio_hardware.h"
 
 #include "base/logging.h"
 #include "content/common/view_messages.h"
 #include "content/renderer/render_thread_impl.h"
 
@@ skipping 30 matching lines @@
   if (!output_buffer_size) {
     uint32 buffer_size = 0;
     RenderThreadImpl::current()->Send(
         new ViewHostMsg_GetHardwareBufferSize(&buffer_size));
     output_buffer_size = buffer_size;
   }
 
   return output_buffer_size;
 }
 
+size_t GetHighLatencyOutputBufferSize(int sample_rate) {
+  // The minimum number of samples in a hardware packet.
+  // This value is selected so that we can handle down to 5khz sample rate.
+  static const size_t kMinSamplesPerHardwarePacket = 1024;
+
+  // The maximum number of samples in a hardware packet.
+  // This value is selected so that we can handle up to 192khz sample rate.
+  static const size_t kMaxSamplesPerHardwarePacket = 64 * 1024;
+
+  // This constant governs the hardware audio buffer size, this value should be
+  // chosen carefully.
+  // This value is selected so that we have 8192 samples for 48khz streams.
+  static const size_t kMillisecondsPerHardwarePacket = 170;
+
+  // Select the number of samples that can provide at least
+  // |kMillisecondsPerHardwarePacket| worth of audio data.
+  size_t samples = kMinSamplesPerHardwarePacket;
+  while (samples <= kMaxSamplesPerHardwarePacket &&
+         samples * base::Time::kMillisecondsPerSecond <
+         sample_rate * kMillisecondsPerHardwarePacket) {
+    samples *= 2;
+  }
+  return samples;
+}
+
 uint32 GetInputChannelCount() {
   DCHECK(RenderThreadImpl::current() != NULL);
 
   if (!input_channel_count) {
     uint32 channels = 0;
     RenderThreadImpl::current()->Send(
         new ViewHostMsg_GetHardwareInputChannelCount(&channels));
     input_channel_count = channels;
   }
 
   return input_channel_count;
 }
 
 void ResetCache() {
   DCHECK(RenderThreadImpl::current() != NULL);
 
   output_sample_rate = 0.0;
   input_sample_rate = 0.0;
   output_buffer_size = 0;
   input_channel_count = 0;
 }
 
 }  // namespace audio_hardware