Split audio mixer into interface and implementation.

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 : public rtc::RefCountInterface {
- public:
-  // 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() {}
-  };
-
-  // Since the mixer is reference counted, the destructor may be
-  // called from any thread.
-  ~AudioMixer() override {}
-
-  // 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_