/**
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* Copyright (c) 2022 Xiaomi Corporation (authors: Fangjun Kuang)
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*
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* See LICENSE for clarification regarding multiple authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// The content in this file is copied/modified from
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// This file is copied/modified from kaldi/src/feat/online-feature.h
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#ifndef KALDI_NATIVE_FBANK_CSRC_ONLINE_FEATURE_H_
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#define KALDI_NATIVE_FBANK_CSRC_ONLINE_FEATURE_H_
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#include <cstdint>
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#include <deque>
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#include <vector>
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#include "kaldi-native-fbank/csrc/feature-fbank.h"
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namespace knf {
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/// This class serves as a storage for feature vectors with an option to limit
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/// the memory usage by removing old elements. The deleted frames indices are
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/// "remembered" so that regardless of the MAX_ITEMS setting, the user always
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/// provides the indices as if no deletion was being performed.
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/// This is useful when processing very long recordings which would otherwise
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/// cause the memory to eventually blow up when the features are not being
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/// removed.
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class RecyclingVector {
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public:
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/// By default it does not remove any elements.
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explicit RecyclingVector(int32_t items_to_hold = -1);
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~RecyclingVector() = default;
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RecyclingVector(const RecyclingVector &) = delete;
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RecyclingVector &operator=(const RecyclingVector &) = delete;
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// The pointer is owned by RecyclingVector
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// Users should not free it
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const float *At(int32_t index) const;
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void PushBack(std::vector<float> item);
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/// This method returns the size as if no "recycling" had happened,
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/// i.e. equivalent to the number of times the PushBack method has been
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/// called.
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int32_t Size() const;
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private:
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std::deque<std::vector<float>> items_;
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int32_t items_to_hold_;
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int32_t first_available_index_;
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};
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/// This is a templated class for online feature extraction;
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/// it's templated on a class like MfccComputer or PlpComputer
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/// that does the basic feature extraction.
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template <class C>
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class OnlineGenericBaseFeature {
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public:
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// Constructor from options class
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explicit OnlineGenericBaseFeature(const typename C::Options &opts);
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int32_t Dim() const { return computer_.Dim(); }
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float FrameShiftInSeconds() const {
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return computer_.GetFrameOptions().frame_shift_ms / 1000.0f;
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}
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int32_t NumFramesReady() const { return features_.Size(); }
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// Note: IsLastFrame() will only ever return true if you have called
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// InputFinished() (and this frame is the last frame).
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bool IsLastFrame(int32_t frame) const {
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return input_finished_ && frame == NumFramesReady() - 1;
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}
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const float *GetFrame(int32_t frame) const { return features_.At(frame); }
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// This would be called from the application, when you get
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// more wave data. Note: the sampling_rate is only provided so
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// the code can assert that it matches the sampling rate
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// expected in the options.
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//
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// @param sampling_rate The sampling_rate of the input waveform
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// @param waveform Pointer to a 1-D array of size n
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// @param n Number of entries in waveform
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void AcceptWaveform(float sampling_rate, const float *waveform, int32_t n);
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// InputFinished() tells the class you won't be providing any
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// more waveform. This will help flush out the last frame or two
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// of features, in the case where snip-edges == false; it also
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// affects the return value of IsLastFrame().
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void InputFinished();
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private:
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// This function computes any additional feature frames that it is possible to
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// compute from 'waveform_remainder_', which at this point may contain more
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// than just a remainder-sized quantity (because AcceptWaveform() appends to
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// waveform_remainder_ before calling this function). It adds these feature
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// frames to features_, and shifts off any now-unneeded samples of input from
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// waveform_remainder_ while incrementing waveform_offset_ by the same amount.
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void ComputeFeatures();
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C computer_; // class that does the MFCC or PLP or filterbank computation
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FeatureWindowFunction window_function_;
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// features_ is the Mfcc or Plp or Fbank features that we have already
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// computed.
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RecyclingVector features_;
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// True if the user has called "InputFinished()"
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bool input_finished_;
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// waveform_offset_ is the number of samples of waveform that we have
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// already discarded, i.e. that were prior to 'waveform_remainder_'.
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int64_t waveform_offset_;
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// waveform_remainder_ is a short piece of waveform that we may need to keep
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// after extracting all the whole frames we can (whatever length of feature
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// will be required for the next phase of computation).
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// It is a 1-D tensor
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std::vector<float> waveform_remainder_;
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};
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using OnlineFbank = OnlineGenericBaseFeature<FbankComputer>;
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} // namespace knf
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#endif // KALDI_NATIVE_FBANK_CSRC_ONLINE_FEATURE_H_
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