Optionally disable APM limiter in AudioMixer.

webrtc/modules/audio_mixer/frame_combiner.h

+/*
+ *  Copyright (c) 2017 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_FRAME_COMBINER_H_
+#define WEBRTC_MODULES_AUDIO_MIXER_FRAME_COMBINER_H_
+
+#include <memory>
+#include <vector>
+
+#include "webrtc/modules/audio_processing/include/audio_processing.h"
+#include "webrtc/modules/include/module_common_types.h"
+
+namespace webrtc {

[ivoc, 2017/02/15 16:58:47]

Please insert a blank line below. (between namespace and the class definition)

[aleloi, 2017/02/16 14:01:36]

Done.

+class FrameCombiner {
+ public:
+  explicit FrameCombiner(bool use_apm_limiter);
+  ~FrameCombiner();
+
+  // Combine several frames into one. Assumes sample_rate,
+  // samples_per_channel of the input frames match the parameters. The
+  // extra parameters are needed because 'mix_list' can be empty.
+  void Combine(const std::vector<AudioFrame*>& mix_list,

[ivoc, 2017/02/15 16:58:47]

Can the function be const?

[aleloi, 2017/02/16 14:01:36]

Yes, thank you! CombineMultipleFrames too. They can't be static though, because
of use_apm_limiter_.

+               size_t number_of_channels,
+               int sample_rate,
+               AudioFrame* audio_frame_for_mixing);
+
+ private:
+  // Lower-level helper function called from Combine(...) when there
+  // are several input frames.
+  //
+  // TODO(aleloi): change interface to ArrayView<int16_t> output_frame
+  // once we have gotten rid of the APM limiter.
+  //
+  // Only the 'data' field of output_frame should be modified. The
+  // rest are used for potentially sending the output to the APM
+  // limiter.
+  void CombineMultipleFrames(
+      const std::vector<rtc::ArrayView<const int16_t>>& input_frames,
+      AudioFrame* audio_frame_for_mixing);
+
+  const bool use_apm_limiter_;
+  std::unique_ptr<AudioProcessing> limiter_;
+};
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_MIXER_FRAME_COMBINER_H_