Allow pass through buffer sizes on OSX.

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 <CoreAudio/AudioHardware.h>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 11 matching lines @@
 #include "media/base/bind_to_current_loop.h"
 #include "media/base/channel_layout.h"
 #include "media/base/limits.h"
 #include "media/base/media_switches.h"
 
 namespace media {
 
 // Maximum number of output streams that can be open simultaneously.
 static const int kMaxOutputStreams = 50;
 
-// Default buffer size in samples for low-latency input and output streams.
-static const int kDefaultLowLatencyBufferSize = 128;
+// 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;
 
 static bool HasAudioHardware(AudioObjectPropertySelector selector) {
   AudioDeviceID output_device_id = kAudioObjectUnknown;
   const AudioObjectPropertyAddress property_address = {
     selector,
     kAudioObjectPropertyScopeGlobal,            // mScope
     kAudioObjectPropertyElementMaster           // mElement
@@ skipping 621 matching lines @@
   const AudioDeviceID device = GetAudioDeviceIdByUId(false, output_device_id);
   if (device == kAudioObjectUnknown) {
     DLOG(ERROR) << "Invalid output device " << output_device_id;
     return input_params.IsValid() ? input_params : AudioParameters(
         AudioParameters::AUDIO_PCM_LOW_LATENCY, CHANNEL_LAYOUT_STEREO,
         kFallbackSampleRate, 16, ChooseBufferSize(kFallbackSampleRate));
   }
 
   const bool has_valid_input_params = input_params.IsValid();
   const int hardware_sample_rate = HardwareSampleRateForDevice(device);
-  const int buffer_size = ChooseBufferSize(hardware_sample_rate);
+
+  // 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(hardware_sample_rate);
+  if (has_valid_input_params) {
+    buffer_size =
+        std::min(kMaximumInputOutputBufferSize,
+                 std::max(input_params.frames_per_buffer(), buffer_size));
+  }
 
   int hardware_channels;
   if (!GetDeviceChannels(device, kAudioDevicePropertyScopeOutput,
                          &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.
@@ skipping 54 matching lines @@
   if (current_sample_rate_ == new_sample_rate &&
       current_output_device_ == new_output_device)
     return;
 
   current_sample_rate_ = new_sample_rate;
   current_output_device_ = new_output_device;
   NotifyAllOutputDeviceChangeListeners();
 }
 
 int AudioManagerMac::ChooseBufferSize(int output_sample_rate) {
-  int buffer_size = kDefaultLowLatencyBufferSize;
+  int buffer_size = kMinimumInputOutputBufferSize;
   const int user_buffer_size = GetUserBufferSize();
   if (user_buffer_size) {
     buffer_size = user_buffer_size;
   } else if (output_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 (output_sample_rate <= 96000)
-      buffer_size = 2 * kDefaultLowLatencyBufferSize;
+      buffer_size = 2 * kMinimumInputOutputBufferSize;
     else if (output_sample_rate <= 192000)
-      buffer_size = 4 * kDefaultLowLatencyBufferSize;
+      buffer_size = 4 * kMinimumInputOutputBufferSize;
   }
 
   return buffer_size;
 }
 
 bool AudioManagerMac::ShouldDeferStreamStart() {
   DCHECK(GetTaskRunner()->BelongsToCurrentThread());
   return power_observer_->ShouldDeferStreamStart();
 }
 
 void AudioManagerMac::ReleaseOutputStream(AudioOutputStream* stream) {
   output_streams_.remove(stream);
   AudioManagerBase::ReleaseOutputStream(stream);
 }
 
 void AudioManagerMac::ReleaseInputStream(AudioInputStream* stream) {
   input_streams_.remove(stream);
   AudioManagerBase::ReleaseInputStream(stream);
 }
 
 AudioManager* CreateAudioManager(AudioLogFactory* audio_log_factory) {
   return new AudioManagerMac(audio_log_factory);
 }
 
 }  // namespace media