Use AudioUnit instead of AudioDevice properties to get channel count.

media/audio/mac/scoped_audio_unit.cc

+// Copyright 2017 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/scoped_audio_unit.h"
+
+#include "base/mac/mac_logging.h"
+
+namespace media {
+
+constexpr AudioComponentDescription desc = {kAudioUnitType_Output,
+                                            kAudioUnitSubType_HALOutput,
+                                            kAudioUnitManufacturer_Apple, 0, 0};
+
+static void DestroyAudioUnit(AudioUnit audio_unit) {
+  OSStatus result = AudioUnitUninitialize(audio_unit);
+  OSSTATUS_DLOG_IF(ERROR, result != noErr, result)
+      << "AudioUnitUninitialize() failed : " << audio_unit;
+  result = AudioComponentInstanceDispose(audio_unit);
+  OSSTATUS_DLOG_IF(ERROR, result != noErr, result)
+      << "AudioComponentInstanceDispose() failed : " << audio_unit;
+}
+
+ScopedAudioUnit::ScopedAudioUnit(AudioDeviceID device, AUElement element) {
+  AudioComponent comp = AudioComponentFindNext(0, &desc);
+  if (!comp)
+    return;
+
+  AudioUnit audio_unit;
+  OSStatus result = AudioComponentInstanceNew(comp, &audio_unit);
+  if (result != noErr) {
+    OSSTATUS_DLOG(ERROR, result) << "AudioComponentInstanceNew() failed.";
+    return;
+  }
+
+  result = AudioUnitSetProperty(
+      audio_unit, kAudioOutputUnitProperty_CurrentDevice,
+      kAudioUnitScope_Global, element, &device, sizeof(AudioDeviceID));
+  if (result == noErr) {
+    audio_unit_ = audio_unit;
+    return;
+  }
+  OSSTATUS_DLOG(ERROR, result)
+      << "Failed to set current device for audio unit.";
+  DestroyAudioUnit(audio_unit);
+}
+
+ScopedAudioUnit::~ScopedAudioUnit() {
+  if (audio_unit_)
+    DestroyAudioUnit(audio_unit_);
+}
+
+}  // namespace media