media/audio/audio_output_proxy.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_AUDIO_AUDIO_OUTPUT_PROXY_H_
   6 #define MEDIA_AUDIO_AUDIO_OUTPUT_PROXY_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/task.h"
  10 #include "media/audio/audio_io.h"
  11 #include "media/audio/audio_parameters.h"
  12
  13 class AudioOutputDispatcher;
  14
  15 // AudioOutputProxy is an audio otput stream that uses resources more
  16 // efficiently than a regular audio output stream: it opens audio
  17 // device only when sound is playing, i.e. between Start() and Stop()
  18 // (there is still one physical stream per each audio output proxy in
  19 // playing state).
  20 //
  21 // AudioOutputProxy uses AudioOutputDispatcher to open and close
  22 // physical output streams.
  23 class MEDIA_EXPORT AudioOutputProxy : public AudioOutputStream {
  24  public:
  25   // Caller keeps ownership of |dispatcher|.
  26   explicit AudioOutputProxy(AudioOutputDispatcher* dispatcher);
  27
  28   // AudioOutputStream interface.
  29   virtual bool Open() OVERRIDE;
  30   virtual void Start(AudioSourceCallback* callback) OVERRIDE;
  31   virtual void Stop() OVERRIDE;
  32   virtual void SetVolume(double volume) OVERRIDE;
  33   virtual void GetVolume(double* volume) OVERRIDE;
  34   virtual void Close() OVERRIDE;
  35
  36  private:
  37   enum State {
  38     kCreated,
  39     kOpened,
  40     kPlaying,
  41     kClosed,
  42     kError,
  43   };
  44
  45   virtual ~AudioOutputProxy();
  46
  47   scoped_refptr<AudioOutputDispatcher> dispatcher_;
  48   State state_;
  49
  50   // The actual audio stream. Must be set to NULL in any state other
  51   // than kPlaying.
  52   AudioOutputStream* physical_stream_;
  53
  54   // Need to save volume here, so that we can restore it in case the stream
  55   // is stopped, and then started again.
  56   double volume_;
  57
  58   DISALLOW_COPY_AND_ASSIGN(AudioOutputProxy);
  59 };
  60
  61 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_PROXY_H_