Send data from mixer to APM limiter more often.

webrtc/modules/audio_mixer/gain_change_calculator.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_GAIN_CHANGE_CALCULATOR_H_
+#define WEBRTC_MODULES_AUDIO_MIXER_GAIN_CHANGE_CALCULATOR_H_
+
+#include "webrtc/base/array_view.h"
+
+namespace webrtc {
+
+class GainChangeCalculator {
+ public:
+  // The 'out' signal is assumed to be produced from 'in' by applying
+  // a smoothly varying gain. This method computes variations of the
+  // gain and handles special cases when the samples are small.
+  float CalculateGainChange(rtc::ArrayView<const int16_t> in,
+                            rtc::ArrayView<const int16_t> out);
+
+ private:
+  void CalculateGain(rtc::ArrayView<const int16_t> in,
+                     rtc::ArrayView<const int16_t> out,
+                     rtc::ArrayView<float> gain);
+
+  float CalculateDifferences(rtc::ArrayView<const float> values);
+  float last_value_ = 0.f;
+  float last_reliable_gain_ = 1.0f;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_MIXER_GAIN_CHANGE_CALCULATOR_H_