Make OS audio buffer size limits visible.

media/audio/mac/audio_manager_mac.cc

 // 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.
 
 #include "media/audio/mac/audio_manager_mac.h"
 
 #include <algorithm>
 #include <limits>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/mac/mac_logging.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/macros.h"
 #include "base/memory/free_deleter.h"
 #include "base/power_monitor/power_monitor.h"
 #include "base/power_monitor/power_observer.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/threading/thread_checker.h"
 #include "media/audio/audio_device_description.h"
 #include "media/audio/mac/audio_auhal_mac.h"
 #include "media/audio/mac/audio_input_mac.h"
 #include "media/audio/mac/audio_low_latency_input_mac.h"
 #include "media/audio/mac/scoped_audio_unit.h"
 #include "media/base/audio_parameters.h"
 #include "media/base/bind_to_current_loop.h"
 #include "media/base/channel_layout.h"
 #include "media/base/limits.h"
+#include "media/base/mac/audio_util_mac.h"
 #include "media/base/media_switches.h"
 
 namespace media {
 
 // Maximum number of output streams that can be open simultaneously.
 static const int kMaxOutputStreams = 50;
 
-// Define bounds for for low-latency input and output streams.
-static const int kMinimumInputOutputBufferSize = 128;
-static const int kMaximumInputOutputBufferSize = 4096;
-
 // Default sample-rate on most Apple hardware.
 static const int kFallbackSampleRate = 44100;
 
 // Helper method to construct AudioObjectPropertyAddress structure given
 // property selector and scope. The property element is always set to
 // kAudioObjectPropertyElementMaster.
 static AudioObjectPropertyAddress GetAudioObjectPropertyAddress(
     AudioObjectPropertySelector selector,
     bool is_input) {
   AudioObjectPropertyScope scope = is_input ? kAudioObjectPropertyScopeInput
@@ skipping 778 matching lines @@
         AudioParameters::AUDIO_PCM_LOW_LATENCY, CHANNEL_LAYOUT_STEREO,
         kFallbackSampleRate, 16, ChooseBufferSize(false, kFallbackSampleRate));
   }
 
   const bool has_valid_input_params = input_params.IsValid();
   const int hardware_sample_rate = HardwareSampleRateForDevice(device);
 
   // Allow pass through buffer sizes.  If concurrent input and output streams
   // exist, they will use the smallest buffer size amongst them.  As such, each
   // stream must be able to FIFO requests appropriately when this happens.
-  int buffer_size = ChooseBufferSize(false, hardware_sample_rate);
-  if (has_valid_input_params) {
-    buffer_size =
-        std::min(kMaximumInputOutputBufferSize,
-                 std::max(input_params.frames_per_buffer(), buffer_size));
-  }
+  int buffer_size =

[DaleCurtis, 2017/06/27 17:25:08]

Might be worth breaking this out of a ternary for clarity.

[Andrew MacPherson, 2017/06/27 17:46:49]

Done.

+      has_valid_input_params
+          // If passed in via the input_params we allow buffer sizes to go as
+          // low as the the kMinAudioBufferSize, ignoring what
+          // ChooseBufferSize() normally returns.
+          ? std::min(static_cast<int>(limits::kMaxAudioBufferSize),
+                     std::max(input_params.frames_per_buffer(),
+                              static_cast<int>(limits::kMinAudioBufferSize)))
+          : ChooseBufferSize(false, hardware_sample_rate);
 
   int hardware_channels;
   if (!GetDeviceChannels(device, AUElement::OUTPUT, &hardware_channels))
     hardware_channels = 2;
 
   // Use the input channel count and channel layout if possible.  Let OSX take
   // care of remapping the channels; this lets user specified channel layouts
   // work correctly.
   int output_channels = input_params.channels();
   ChannelLayout channel_layout = input_params.channel_layout();
@@ skipping 25 matching lines @@
       current_output_device_ == new_output_device) {
     return;
   }
 
   current_sample_rate_ = new_sample_rate;
   current_output_device_ = new_output_device;
   NotifyAllOutputDeviceChangeListeners();
 }
 
 int AudioManagerMac::ChooseBufferSize(bool is_input, int sample_rate) {
-  // kMinimumInputOutputBufferSize is too small for the output side because
+  // kMinAudioBufferSize is too small for the output side because
   // CoreAudio can get into under-run if the renderer fails delivering data
   // to the browser within the allowed time by the OS. The workaround is to
   // use 256 samples as the default output buffer size for sample rates
   // smaller than 96KHz.
   // TODO(xians): Remove this workaround after WebAudio supports user defined
   // buffer size.  See https://github.com/WebAudio/web-audio-api/issues/348
   // for details.
-  int buffer_size = is_input ?
-      kMinimumInputOutputBufferSize : 2 * kMinimumInputOutputBufferSize;
+  int buffer_size =
+      is_input ? limits::kMinAudioBufferSize : 2 * limits::kMinAudioBufferSize;
   const int user_buffer_size = GetUserBufferSize();
-  if (user_buffer_size) {
-    buffer_size = user_buffer_size;
-  } else if (sample_rate > 48000) {
-    // The default buffer size is too small for higher sample rates and may lead
-    // to glitching.  Adjust upwards by multiples of the default size.
-    if (sample_rate <= 96000)
-      buffer_size = 2 * kMinimumInputOutputBufferSize;
-    else if (sample_rate <= 192000)
-      buffer_size = 4 * kMinimumInputOutputBufferSize;
-  }
-
+  buffer_size = user_buffer_size
+                    ? user_buffer_size
+                    : audio_util_mac::GetMinAudioBufferSizeForSampleRate(
+                          buffer_size, sample_rate);
   return buffer_size;
 }
 
 bool AudioManagerMac::IsSuspending() const {
   DCHECK(GetTaskRunner()->BelongsToCurrentThread());
   return power_observer_->IsSuspending();
 }
 
 bool AudioManagerMac::ShouldDeferStreamStart() const {
   DCHECK(GetTaskRunner()->BelongsToCurrentThread());
@@ skipping 261 matching lines @@
 }
 
 std::unique_ptr<AudioManager> CreateAudioManager(
     std::unique_ptr<AudioThread> audio_thread,
     AudioLogFactory* audio_log_factory) {
   return base::MakeUnique<AudioManagerMac>(std::move(audio_thread),
                                            audio_log_factory);
 }
 
 }  // namespace media