Split audio mixer into interface and implementation.

webrtc/api/audio/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_
+#ifndef WEBRTC_API_AUDIO_AUDIO_MIXER_H_
+#define WEBRTC_API_AUDIO_AUDIO_MIXER_H_
 
 #include <memory>

[the sun, 2016/10/20 09:13:05]

not needed?

[aleloi, 2016/10/20 09:35:18]

There is a unique_ptr<AudioProcessing> argument to the constructor.

 
 #include "webrtc/base/refcount.h"
 #include "webrtc/modules/include/module_common_types.h"
 
 namespace webrtc {
 
+// WORK IN PROGRESS

[kwiberg-webrtc, 2016/10/20 09:24:12]

Are we allowed to use Unicode in source files yet? If so, consider adding a 🚧
(U+1F6A7, "Construction Sign").

[aleloi, 2016/10/20 09:35:18]

Hm... I wonder what that will do to peoples editors... I think I'll stick to
convention and custom :)

+// This class is under development and is not yet intended for for use outside
+// of WebRtc/Libjingle.
 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.
+      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,   // The 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;
+    // A way for a mixer implementation to 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.

[the sun, 2016/10/20 09:13:05]

Why isn't the information in AudioFrame used? (Sorry, I feel I've asked this
before)

[aleloi, 2016/10/20 09:35:18]

Yes, I also think that we had this discussion a while ago (can't remember
where). It's for readability and simplicity: now AudioFrame is output-only.
Instead of having to specify in the interface that some fields are valid and
others are not, we just say that all fields  of |audio_frame_...| must be
overwritten.

   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_
+#endif  // WEBRTC_API_AUDIO_AUDIO_MIXER_H_