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// Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
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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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// itf/decodable-itf.h
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// Copyright 2009-2011 Microsoft Corporation; Saarland University;
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@ -56,10 +42,8 @@ namespace kaldi {
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For online decoding, where the features are coming in in real time, it is
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important to understand the IsLastFrame() and NumFramesReady() functions.
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There are two ways these are used: the old online-decoding code, in
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../online/,
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and the new online-decoding code, in ../online2/. In the old
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online-decoding
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There are two ways these are used: the old online-decoding code, in ../online/,
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and the new online-decoding code, in ../online2/. In the old online-decoding
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code, the decoder would do:
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\code{.cc}
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for (int frame = 0; !decodable.IsLastFrame(frame); frame++) {
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@ -68,16 +52,13 @@ namespace kaldi {
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\endcode
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and the call to IsLastFrame would block if the features had not arrived yet.
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The decodable object would have to know when to terminate the decoding. This
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online-decoding mode is still supported, it is what happens when you call,
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for
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online-decoding mode is still supported, it is what happens when you call, for
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example, LatticeFasterDecoder::Decode().
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We realized that this "blocking" mode of decoding is not very convenient
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because it forces the program to be multi-threaded and makes it complex to
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control endpointing. In the "new" decoding code, you don't call (for
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example)
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LatticeFasterDecoder::Decode(), you call
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LatticeFasterDecoder::InitDecoding(),
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control endpointing. In the "new" decoding code, you don't call (for example)
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LatticeFasterDecoder::Decode(), you call LatticeFasterDecoder::InitDecoding(),
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and then each time you get more features, you provide them to the decodable
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object, and you call LatticeFasterDecoder::AdvanceDecoding(), which does
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something like this:
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@ -87,8 +68,7 @@ namespace kaldi {
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}
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\endcode
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So the decodable object never has IsLastFrame() called. For decoding where
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you are starting with a matrix of features, the NumFramesReady() function
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will
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you are starting with a matrix of features, the NumFramesReady() function will
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always just return the number of frames in the file, and IsLastFrame() will
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return true for the last frame.
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@ -100,52 +80,45 @@ namespace kaldi {
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frame of the file once we've decided to terminate decoding.
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*/
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class DecodableInterface {
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public:
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/// Returns the log likelihood, which will be negated in the decoder.
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/// The "frame" starts from zero. You should verify that NumFramesReady() >
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/// frame
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/// before calling this.
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virtual BaseFloat LogLikelihood(int32 frame, int32 index) = 0;
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/// Returns true if this is the last frame. Frames are zero-based, so the
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/// first frame is zero. IsLastFrame(-1) will return false, unless the file
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/// is empty (which is a case that I'm not sure all the code will handle, so
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/// be careful). Caution: the behavior of this function in an online
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/// setting
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/// is being changed somewhat. In future it may return false in cases where
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/// we haven't yet decided to terminate decoding, but later true if we
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/// decide
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/// to terminate decoding. The plan in future is to rely more on
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/// NumFramesReady(), and in future, IsLastFrame() would always return false
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/// in an online-decoding setting, and would only return true in a
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/// decoding-from-matrix setting where we want to allow the last delta or
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/// LDA
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/// features to be flushed out for compatibility with the baseline setup.
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virtual bool IsLastFrame(int32 frame) const = 0;
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/// The call NumFramesReady() will return the number of frames currently
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/// available
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/// for this decodable object. This is for use in setups where you don't
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/// want the
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/// decoder to block while waiting for input. This is newly added as of Jan
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/// 2014,
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/// and I hope, going forward, to rely on this mechanism more than
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/// IsLastFrame to
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/// know when to stop decoding.
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virtual int32 NumFramesReady() const {
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KALDI_ERR
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<< "NumFramesReady() not implemented for this decodable type.";
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return -1;
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}
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/// Returns the number of states in the acoustic model
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/// (they will be indexed one-based, i.e. from 1 to NumIndices();
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/// this is for compatibility with OpenFst).
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virtual int32 NumIndices() const = 0;
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virtual std::vector<BaseFloat> FrameLogLikelihood(int32 frame) = 0;
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virtual ~DecodableInterface() {}
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public:
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/// Returns the log likelihood, which will be negated in the decoder.
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/// The "frame" starts from zero. You should verify that NumFramesReady() > frame
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/// before calling this.
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virtual BaseFloat LogLikelihood(int32 frame, int32 index) = 0;
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/// Returns true if this is the last frame. Frames are zero-based, so the
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/// first frame is zero. IsLastFrame(-1) will return false, unless the file
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/// is empty (which is a case that I'm not sure all the code will handle, so
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/// be careful). Caution: the behavior of this function in an online setting
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/// is being changed somewhat. In future it may return false in cases where
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/// we haven't yet decided to terminate decoding, but later true if we decide
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/// to terminate decoding. The plan in future is to rely more on
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/// NumFramesReady(), and in future, IsLastFrame() would always return false
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/// in an online-decoding setting, and would only return true in a
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/// decoding-from-matrix setting where we want to allow the last delta or LDA
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/// features to be flushed out for compatibility with the baseline setup.
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virtual bool IsLastFrame(int32 frame) const = 0;
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/// The call NumFramesReady() will return the number of frames currently available
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/// for this decodable object. This is for use in setups where you don't want the
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/// decoder to block while waiting for input. This is newly added as of Jan 2014,
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/// and I hope, going forward, to rely on this mechanism more than IsLastFrame to
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/// know when to stop decoding.
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virtual int32 NumFramesReady() const {
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KALDI_ERR << "NumFramesReady() not implemented for this decodable type.";
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return -1;
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}
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/// Returns the number of states in the acoustic model
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/// (they will be indexed one-based, i.e. from 1 to NumIndices();
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/// this is for compatibility with OpenFst).
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virtual int32 NumIndices() const = 0;
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virtual bool FrameLogLikelihood(int32 frame,
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std::vector<kaldi::BaseFloat>* likelihood) = 0;
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virtual ~DecodableInterface() {}
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};
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/// @}
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} // namespace Kaldi
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Yang Zhou
2 years ago