Changed mixing to be done at the minimal possible frequency.

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.
  */
 
@@ skipping 42 matching lines @@
 
   // 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. This method
-  // will only be called from a single thread. The rate and channels
-  // arguments specify the rate and number of channels of the mix
-  // result. All fields in |audio_frame_for_mixing| must be updated.
-  virtual void Mix(int sample_rate_hz,
-                   size_t number_of_channels,
+  // will only be called from a single thread. The channels argument
+  // specifies the number of channels of the mix result. The mixer
+  // should mix at a rate that doesn't cause quality loss of the
+  // sources' audio. All fields in |audio_frame_for_mixing| must be
+  // updated.

[hlundin-webrtc, 2016/10/31 14:14:56]

Will the implementation have to provide the mixed audio in any of the native
rates (8, 16, 32, 48), or can it be any rate?

[aleloi, 2016/10/31 14:35:57]

It must be a native rate, and it must be part of the interface. I've added it in
the next ps.

+  virtual void Mix(size_t number_of_channels,
                    AudioFrame* audio_frame_for_mixing) = 0;
 
  protected:
   // Since the mixer is reference counted, the destructor may be
   // called from any thread.
   ~AudioMixer() override {}
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_AUDIO_AUDIO_MIXER_H_