Pull out the PostFilter to its own NonlinearBeamformer API

webrtc/modules/audio_processing/beamformer/beamformer.h

-/*
- *  Copyright (c) 2015 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_BEAMFORMER_BEAMFORMER_H_
-#define WEBRTC_MODULES_AUDIO_PROCESSING_BEAMFORMER_BEAMFORMER_H_
-
-#include "webrtc/common_audio/channel_buffer.h"
-#include "webrtc/modules/audio_processing/beamformer/array_util.h"
-
-namespace webrtc {
-
-template<typename T>
-class Beamformer {
- public:
-  virtual ~Beamformer() {}
-
-  // Process one time-domain chunk of audio. The audio is expected to be split
-  // into frequency bands inside the ChannelBuffer. The number of frames and
-  // channels must correspond to the constructor parameters. The same
-  // ChannelBuffer can be passed in as |input| and |output|.
-  virtual void ProcessChunk(const ChannelBuffer<T>& input,
-                            ChannelBuffer<T>* output) = 0;
-
-  // Sample rate corresponds to the lower band.
-  // Needs to be called before the the Beamformer can be used.
-  virtual void Initialize(int chunk_size_ms, int sample_rate_hz) = 0;
-
-  // Aim the beamformer at a point in space.
-  virtual void AimAt(const SphericalPointf& spherical_point) = 0;
-
-  // Indicates whether a given point is inside of the beam.
-  virtual bool IsInBeam(const SphericalPointf& spherical_point) { return true; }
-
-  // Returns true if the current data contains the target signal.
-  // Which signals are considered "targets" is implementation dependent.
-  virtual bool is_target_present() = 0;
-};
-
-}  // namespace webrtc
-
-#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_BEAMFORMER_BEAMFORMER_H_