Work on improving PpbAudioConfig:RecommendSampleFrameCount

ppapi/shared_impl/ppb_audio_config_shared.cc

Index: ppapi/shared_impl/ppb_audio_config_shared.cc
===================================================================
--- ppapi/shared_impl/ppb_audio_config_shared.cc	(revision 120806)
+++ ppapi/shared_impl/ppb_audio_config_shared.cc	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -46,6 +46,40 @@
   return object->GetReference();
 }
 
+// static
+uint32_t PPB_AudioConfig_Shared::RecommendSampleFrameCount(
+    PP_AudioSampleRate sample_rate,
+    uint32_t sample_frame_count,
+    PP_AudioSampleRate hardware_sample_rate,
+    uint32_t hardware_sample_frame_count) {
+  if (sample_frame_count < PP_AUDIOMINSAMPLEFRAMECOUNT)
+    sample_frame_count = PP_AUDIOMINSAMPLEFRAMECOUNT;
+  // If client is using same sample rate as audio hardware, then recommend a
+  // multiple of the audio hardware's sample frame count.
+  if (hardware_sample_rate == sample_rate && hardware_sample_frame_count > 0) {
+    // Round up input sample_frame_count to nearest multiple.
+    uint32_t multiple = (sample_frame_count + hardware_sample_frame_count - 1) /
+        hardware_sample_frame_count;
+    uint32_t recommendation = hardware_sample_frame_count * multiple;
+    if (recommendation > PP_AUDIOMAXSAMPLEFRAMECOUNT)
+      recommendation = PP_AUDIOMAXSAMPLEFRAMECOUNT;
+    return recommendation;
+  }
+  // Otherwise, recommend a conservative 30ms buffer based on sample rate.
+  const uint32_t kDefault30msAt44100kHz = 1323;
+  const uint32_t kDefault30msAt48000kHz = 1440;
+  switch (sample_rate) {
+    case PP_AUDIOSAMPLERATE_44100:
+      return kDefault30msAt44100kHz;
+    case PP_AUDIOSAMPLERATE_48000:
+      return kDefault30msAt48000kHz;
+    case PP_AUDIOSAMPLERATE_NONE:
+      return 0;
+  }
+  // Unable to make a recommendation.
+  return 0;
+}
+
 thunk::PPB_AudioConfig_API* PPB_AudioConfig_Shared::AsPPB_AudioConfig_API() {
   return this;
 }