When devices go from one channel to two, resume stereo playout

Previously, if a device (bluetooth) went from two channels playout
to one, it'd stay there even after bluetooth stopped hands-free mode.

This resulted in losing stereo after talking.

Author: roxanneskelly

build/patches/airpod_fixes.patch

@@ -1,7 +1,43 @@
 diff --git a/modules/audio_device/mac/audio_device_mac.cc b/modules/audio_device/mac/audio_device_mac.cc
-index 0a371737b3..e3a902270d 100644
+index 0a371737b3..eb6061a5d9 100644
 --- a/modules/audio_device/mac/audio_device_mac.cc
 +++ b/modules/audio_device/mac/audio_device_mac.cc
+@@ -1043,13 +1043,6 @@ int32_t AudioDeviceMac::InitPlayout() {
+   RTC_LOG(LS_VERBOSE) << "mFormatFlags = " << _outStreamFormat.mFormatFlags;
+   logCAMsg(rtc::LS_VERBOSE, "mFormatID",
+            (const char*)&_outStreamFormat.mFormatID);
+-
+-  // Our preferred format to work with.
+-  if (_outStreamFormat.mChannelsPerFrame < 2) {
+-    // Disable stereo playout when we only have one channel on the device.
+-    _playChannels = 1;
+-    RTC_LOG(LS_VERBOSE) << "Stereo playout unavailable on this device";
+-  }
+   WEBRTC_CA_RETURN_ON_ERR(SetDesiredPlayoutFormat());
+ 
+   // Listen for format changes.
+@@ -1790,12 +1783,19 @@ int32_t AudioDeviceMac::InitDevice(const uint16_t userDeviceIndex,
+ OSStatus AudioDeviceMac::SetDesiredPlayoutFormat() {
+   // Our preferred format to work with.
+   _outDesiredFormat.mSampleRate = N_PLAY_SAMPLES_PER_SEC;
+-  _outDesiredFormat.mChannelsPerFrame = _playChannels;
++  _outDesiredFormat.mChannelsPerFrame = _outStreamFormat.mChannelsPerFrame;
++  if (_playChannels > 1 && _outDesiredFormat.mChannelsPerFrame < 2) {
++      RTC_LOG(LS_VERBOSE) << "Stereo playout unavailable on this device";
++  }
++  if (_outDesiredFormat.mChannelsPerFrame > _playChannels)
++  {
++      _outDesiredFormat.mChannelsPerFrame = _playChannels;
++  }
+ 
+   if (_ptrAudioBuffer) {
+     // Update audio buffer with the selected parameters.
+     _ptrAudioBuffer->SetPlayoutSampleRate(N_PLAY_SAMPLES_PER_SEC);
+-    _ptrAudioBuffer->SetPlayoutChannels((uint8_t)_playChannels);
++    _ptrAudioBuffer->SetPlayoutChannels((uint8_t)_outDesiredFormat.mChannelsPerFrame);
+   }
+ 
+   _renderDelayOffsetSamples =
 @@ -2096,12 +2096,6 @@ int32_t AudioDeviceMac::HandleStreamFormatChange(
      return -1;
    }
@@ -28,3 +64,34 @@ index 0a371737b3..e3a902270d 100644
      const int io_block_size_samples = streamFormat.mChannelsPerFrame *
                                        streamFormat.mSampleRate / 100 *
                                        N_BLOCKS_IO;
+@@ -2144,12 +2144,6 @@ int32_t AudioDeviceMac::HandleStreamFormatChange(
+                                               &_captureConverter));
+   } else {
+     memcpy(&_outStreamFormat, &streamFormat, sizeof(streamFormat));
+-
+-    // Our preferred format to work with
+-    if (_outStreamFormat.mChannelsPerFrame < 2) {
+-      _playChannels = 1;
+-      RTC_LOG(LS_VERBOSE) << "Stereo playout unavailable on this device";
+-    }
+     WEBRTC_CA_RETURN_ON_ERR(SetDesiredPlayoutFormat());
+   }
+   return 0;
+@@ -2262,7 +2256,7 @@ OSStatus AudioDeviceMac::implDeviceIOProc(const AudioBufferList* inputData,
+       if (_twoDevices || (!_recording && !_playing)) {
+         // In the case of a shared device, the single driving ioProc
+         // is stopped here
+-        WEBRTC_CA_LOG_ERR(AudioDeviceStop(_outputDeviceID, _deviceIOProcID));
++        WEBRTC_CA_LOG_WARN(AudioDeviceStop(_outputDeviceID, _deviceIOProcID));
+         WEBRTC_CA_LOG_WARN(
+             AudioDeviceDestroyIOProcID(_outputDeviceID, _deviceIOProcID));
+         if (err == noErr) {
+@@ -2353,7 +2347,7 @@ OSStatus AudioDeviceMac::implInDeviceIOProc(const AudioBufferList* inputData,
+     MutexLock lock(&mutex_);
+     if (_doStopRec) {
+       // This will be signalled only when a shared device is not in use.
+-      WEBRTC_CA_LOG_ERR(AudioDeviceStop(_inputDeviceID, _inDeviceIOProcID));
++      WEBRTC_CA_LOG_WARN(AudioDeviceStop(_inputDeviceID, _inDeviceIOProcID));
+       WEBRTC_CA_LOG_WARN(
+           AudioDeviceDestroyIOProcID(_inputDeviceID, _inDeviceIOProcID));
+       if (err == noErr) {

build/patches/dont_fatal_error_on_audio_device_stop.patch

@@ -221,7 +221,6 @@ def get_depot_tools(source_dir, fetch=False):
         'bug_8759_workaround.patch',
         'disable_mute_of_audio_processing.patch',
         'crash_on_fatal_error.patch',
-        'dont_fatal_error_on_audio_device_stop.patch',
         'airpod_fixes.patch',
     ],
     'macos_arm64': [
@@ -232,7 +231,6 @@ def get_depot_tools(source_dir, fetch=False):
         'bug_8759_workaround.patch',
         'disable_mute_of_audio_processing.patch',
         'crash_on_fatal_error.patch',
-        'dont_fatal_error_on_audio_device_stop.patch',
         'airpod_fixes.patch',
     ],
     'ios': [