Make OS audio buffer size limits visible.

media/audio/mac/audio_manager_mac.cc

Index: media/audio/mac/audio_manager_mac.cc
diff --git a/media/audio/mac/audio_manager_mac.cc b/media/audio/mac/audio_manager_mac.cc
index 09b6433e631d819fc6bc87ab72f4c55b5cc672d1..b4e1dea2bb32dfc7d6c306bbb5c8b531c57ba046 100644
--- a/media/audio/mac/audio_manager_mac.cc
+++ b/media/audio/mac/audio_manager_mac.cc
@@ -27,6 +27,7 @@
 #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 {
@@ -34,10 +35,6 @@ 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;
 
@@ -836,12 +833,15 @@ AudioParameters AudioManagerMac::GetPreferredOutputStreamParameters(
   // 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 =
+      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))
@@ -887,7 +887,7 @@ void AudioManagerMac::HandleDeviceChanges() {
 }
 
 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
@@ -895,20 +895,13 @@ int AudioManagerMac::ChooseBufferSize(bool is_input, int sample_rate) {
   // 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;
 }