implement AudioManagerMac::GetPreferredLowLatencyOutputStreamParameters(

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 edf59930d155f57bda6be85a2a139c4fa3314ad6..a4cadbaa39f6eaa0a5d0dfcd7d4ff5aa85858695 100644
--- a/media/audio/mac/audio_manager_mac.cc
+++ b/media/audio/mac/audio_manager_mac.cc
@@ -10,6 +10,7 @@
 #include "base/mac/mac_logging.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/sys_string_conversions.h"
+#include "media/audio/audio_util.h"
 #include "media/audio/mac/audio_input_mac.h"
 #include "media/audio/mac/audio_low_latency_input_mac.h"
 #include "media/audio/mac/audio_low_latency_output_mac.h"
@@ -25,6 +26,9 @@ namespace media {
 // Maximum number of output streams that can be open simultaneously.
 static const int kMaxOutputStreams = 50;
 
+// Maximum buffer size that CoreAudio can support, used by low latency path.
+static const int kMaxLowLatencyBufferSize = 2047;
+
 static bool HasAudioHardware(AudioObjectPropertySelector selector) {
   AudioDeviceID output_device_id = kAudioObjectUnknown;
   const AudioObjectPropertyAddress property_address = {
@@ -333,4 +337,22 @@ AudioManager* CreateAudioManager() {
   return new AudioManagerMac();
 }
 
+AudioParameters AudioManagerMac::GetPreferredLowLatencyOutputStreamParameters(
+    const AudioParameters& params) {
+  // Applications should use their own preferred buffer size when no resampler
+  // is needed, and Apple CoreAudio can accept any buffer size up to 2047.
+  int native_sample_rate = GetAudioHardwareSampleRate();
+  int buffer_size = GetAudioHardwareBufferSize();
+  if (native_sample_rate == params.sample_rate() &&
+      params.frames_per_buffer() <= kMaxLowLatencyBufferSize) {
+    buffer_size = params.frames_per_buffer();
+  }
+
+  return AudioParameters(AudioParameters::AUDIO_PCM_LOW_LATENCY,
+                         params.channel_layout(),
+                         native_sample_rate,
+                         16,
+                         buffer_size);
+}
+
 }  // namespace media