New module for the adaptive level controlling functionality in the audio processing module

webrtc/modules/audio_processing/level_controller/down_sampler.h

+/*
+ *  Copyright (c) 2016 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_PROCESSING_LEVEL_CONTROLLER_DOWN_SAMPLER_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_DOWN_SAMPLER_H_
+
+#include <memory>
+
+#include "webrtc/base/array_view.h"
+#include "webrtc/base/constructormagic.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+class BiQuadFilter;
+
+class DownSampler {
+ public:
+  DownSampler(ApmDataDumper* data_dumper, int sample_rate_hz);

[hlundin-webrtc, 2016/06/27 11:21:14]

data_dumper is in some sense an output variable, so I think it should go last on
the line.

[peah-webrtc, 2016/06/27 22:51:47]

Done.

+  ~DownSampler();

[hlundin-webrtc, 2016/06/27 11:21:14]

Do you need this? And if so, consider using = defualt inline.

[peah-webrtc, 2016/06/27 22:51:47]

I think it is needed as the ApmDataDumper and BiQuadFilter types are only
specified using forwards. If the default destructor is used, the compilation
fails as the compiler needs to know the sizes of the object when building
down_sampler.h and therefore cannot use forward declarations for the member
types.

At least this is what I think happens, and I cannot get the compile to work when
using default destructor implementations with only forward declarations of the
above types.

Does that make sense, or am I have I missed something in that?

[hlundin-webrtc, 2016/06/28 11:29:00]

Acknowledged.

[peah-webrtc, 2016/06/28 22:19:37]

Acknowledged.

+
+  void DownSample(rtc::ArrayView<const float> in, rtc::ArrayView<float> out);
+
+ private:
+  ApmDataDumper* data_dumper_;
+  const int sample_rate_hz_;
+  std::unique_ptr<BiQuadFilter> low_pass_filter_;
+  int down_sampling_factor_;
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(DownSampler);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_DOWN_SAMPLER_H_