[Chromoting] Audio playback won't work after switching default playback device

remoting/host/audio_capturer_win.h

 // 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.
 
 #ifndef REMOTING_HOST_AUDIO_CAPTURER_WIN_H_
 #define REMOTING_HOST_AUDIO_CAPTURER_WIN_H_
 
 #include <audioclient.h>
 #include <endpointvolume.h>
 #include <mmdeviceapi.h>
@@ skipping 13 matching lines @@
 
 class AudioCapturerWin : public AudioCapturer {
  public:
   AudioCapturerWin();
   ~AudioCapturerWin() override;
 
   // AudioCapturer interface.
   bool Start(const PacketCapturedCallback& callback) override;
 
  private:
+  // An IMMNotificationClient implementation to detect the event of default
+  // audio device recently changed. If it indicates a changed happend recently,
+  // we need to recreate all audio components.
+  class MMNotificationClient;
+
+  // Resets and reinitializes default audio device related components. These
+  // components must be recreated once the default audio device changed. Returns
+  // false if initialization failed.
+  bool ResetAndInitialize();
+
   // Receives all packets from the audio capture endpoint buffer and pushes them
   // to the network.
   void DoCapture();
 
   // Returns current volume setting of the host, in range [0.0, 1.0]. If the
   // audio has been muted, this function returns 0. If Windows API returns error
   // (such as audio device has been disabled or unpluged), this function ignores
   // host volume setting, and returns 1.0.
   float GetAudioLevel();
 
   // Processes a series of samples, and executes callback if the packet is
   // qualified to be sent to client.
   void ProcessSamples(uint8_t* data, size_t frames);
 
   PacketCapturedCallback callback_;
 
   AudioPacket::SamplingRate sampling_rate_;
 
   std::unique_ptr<base::RepeatingTimer> capture_timer_;
   base::TimeDelta audio_device_period_;
 
   AudioSilenceDetector silence_detector_;
 
   base::win::ScopedCoMem<WAVEFORMATEX> wave_format_ex_;
+  base::win::ScopedComPtr<IMMDeviceEnumerator> mm_device_enumerator_;
   base::win::ScopedComPtr<IAudioCaptureClient> audio_capture_client_;
   base::win::ScopedComPtr<IAudioClient> audio_client_;
   base::win::ScopedComPtr<IMMDevice> mm_device_;
   base::win::ScopedComPtr<IAudioEndpointVolume> audio_volume_;
 
+  const std::unique_ptr<MMNotificationClient> mm_notification_client_;
+
   HRESULT last_capture_error_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioCapturerWin);
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_HOST_AUDIO_CAPTURER_WIN_H_