Cleanup of the mixer interface.

webrtc/modules/audio_mixer/audio_mixer.h

 /*
  *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_H_
 #define WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_H_
 
 #include <memory>
 
+#include "webrtc/base/refcount.h"
 #include "webrtc/modules/include/module_common_types.h"
 
 namespace webrtc {
 
-class AudioMixer {
+class AudioMixer : public rtc::RefCountInterface {
  public:
-  static const int kMaximumAmountOfMixedAudioSources = 3;
   // A callback class that all mixer participants must inherit from/implement.
   class Source {
    public:
     enum class AudioFrameInfo {
       kNormal,  // The samples in audio_frame are valid and should be used.
       kMuted,   // The samples in audio_frame should not be used, but should be
       // implicitly interpreted as zero. Other fields in audio_frame
       // may be read and should contain meaningful values.
       kError  // audio_frame will not be used.
     };
 
     struct AudioFrameWithInfo {
       AudioFrame* audio_frame;
       AudioFrameInfo audio_frame_info;
     };
 
     // The implementation of GetAudioFrameWithInfo should update
     // audio_frame with new audio every time it's called. Implementing
     // classes are allowed to return the same AudioFrame pointer on
     // different calls. The pointer must stay valid until the next
     // mixing call or until this audio source is disconnected from the
     // mixer. The mixer may modify the contents of the passed
     // AudioFrame pointer at any time until the next call to
     // GetAudioFrameWithInfo, or until the source is removed from the
     // mixer.
     virtual AudioFrameWithInfo GetAudioFrameWithInfo(int sample_rate_hz) = 0;
 
+    // A way for a mixer implementation do distinguish participants.
+    virtual int ssrc() = 0;
+
    protected:
     virtual ~Source() {}
   };
 
-  // Factory method. Constructor disabled.
-  static std::unique_ptr<AudioMixer> Create();
-  virtual ~AudioMixer() {}
+  // Since the mixer is reference counted, the destructor may be
+  // called from any thread.
+  ~AudioMixer() override {}
 
-  // Add/remove audio sources as candidates for mixing.
-  virtual int32_t SetMixabilityStatus(Source* audio_source, bool mixable) = 0;
+  // Returns true if adding/removing was successful. A source is never
+  // added twice and removal is never attempted if a source has not
+  // been successfully added to the mixer. Addition and removal can
+  // happen on different threads.
+  virtual bool AddSource(Source* audio_source) = 0;
+  virtual bool RemoveSource(Source* audio_source) = 0;
 
   // Performs mixing by asking registered audio sources for audio. The
   // mixed result is placed in the provided AudioFrame. Will only be
   // called from a single thread. The rate and channels arguments
   // specify the rate and number of channels of the mix result.
   virtual void Mix(int sample_rate_hz,
                    size_t number_of_channels,
                    AudioFrame* audio_frame_for_mixing) = 0;
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_H_