lattice-to-nbest.cc
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// latbin/lattice-to-nbest.cc
// Copyright 2009-2012 Stefan Kombrink Johns Hopkins University (Author: Daniel Povey)
// See ../../COPYING for clarification regarding multiple authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// THIS CODE IS PROVIDED *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED
// WARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE,
// MERCHANTABLITY OR NON-INFRINGEMENT.
// See the Apache 2 License for the specific language governing permissions and
// limitations under the License.
#include "base/kaldi-common.h"
#include "util/common-utils.h"
#include "fstext/fstext-lib.h"
#include "lat/kaldi-lattice.h"
int main(int argc, char *argv[]) {
try {
using namespace kaldi;
typedef kaldi::int32 int32;
typedef kaldi::int64 int64;
using fst::SymbolTable;
using fst::VectorFst;
using fst::StdArc;
const char *usage =
"Work out N-best paths in lattices and write out as FSTs\n"
"Note: only guarantees distinct word sequences if distinct paths in\n"
"input lattices had distinct word-sequences (this will not be true if\n"
"you produced lattices with --determinize-lattice=false, i.e. state-level\n"
"lattices).\n"
"Usage: lattice-to-nbest [options] <lattice-rspecifier> <lattice-wspecifier>\n"
" e.g.: lattice-to-nbest --acoustic-scale=0.1 --n=10 ark:1.lats ark:nbest.lats\n";
ParseOptions po(usage);
BaseFloat acoustic_scale = 1.0, lm_scale = 1.0;
bool random = false;
int32 srand_seed = 0;
int32 n = 1;
po.Register("acoustic-scale", &acoustic_scale, "Scaling factor for acoustic likelihoods");
po.Register("lm-scale", &lm_scale, "Scaling factor for language model scores.");
po.Register("n", &n, "Number of distinct paths");
po.Register("random", &random,
"If true, generate n random paths instead of n-best paths"
"In this case, all costs in generated paths will be zero.");
po.Register("srand", &srand_seed, "Seed for random number generator "
"(only relevant if --random=true)");
po.Read(argc, argv);
KALDI_ASSERT(n > 0);
srand(srand_seed);
if (po.NumArgs() != 2) {
po.PrintUsage();
exit(1);
}
std::string lats_rspecifier = po.GetArg(1),
lats_wspecifier = po.GetArg(2);
// Read as regular lattice.
SequentialLatticeReader lattice_reader(lats_rspecifier);
// Write as compact lattice.
CompactLatticeWriter compact_nbest_writer(lats_wspecifier);
int32 n_done = 0;
int64 n_paths_out = 0;
if (acoustic_scale == 0.0 || lm_scale == 0.0)
KALDI_ERR << "Do not use a zero acoustic or LM scale (cannot be inverted)";
for (; !lattice_reader.Done(); lattice_reader.Next()) {
std::string key = lattice_reader.Key();
Lattice lat = lattice_reader.Value();
lattice_reader.FreeCurrent();
fst::ScaleLattice(fst::LatticeScale(lm_scale, acoustic_scale), &lat);
std::vector<Lattice> nbest_lats;
{
Lattice nbest_lat;
if (!random) {
fst::ShortestPath(lat, &nbest_lat, n);
} else {
fst::UniformArcSelector<LatticeArc> uniform_selector;
fst::RandGenOptions<fst::UniformArcSelector<LatticeArc> > opts(uniform_selector);
opts.npath = n;
fst::RandGen(lat, &nbest_lat, opts);
}
fst::ConvertNbestToVector(nbest_lat, &nbest_lats);
}
if (nbest_lats.empty()) {
KALDI_WARN << "Possibly empty lattice for utterance-id " << key
<< "(no N-best entries)";
} else {
for (int32 k = 0; k < static_cast<int32>(nbest_lats.size()); k++) {
std::ostringstream s;
s << key << "-" << (k+1); // so if key is "utt_id", the keys
// of the n-best are utt_id-1, utt_id-2, utt_id-3, etc.
std::string nbest_key = s.str();
fst::ScaleLattice(fst::LatticeScale(1.0/lm_scale, 1.0/acoustic_scale),
&(nbest_lats[k]));
CompactLattice nbest_clat;
ConvertLattice(nbest_lats[k], &nbest_clat); // write in compact form.
compact_nbest_writer.Write(nbest_key, nbest_clat);
}
n_done++;
n_paths_out += nbest_lats.size();
}
}
KALDI_LOG << "Done applying N-best algorithm to " << n_done << " lattices with n = "
<< n << ", average actual #paths is "
<< (n_paths_out/(n_done+1.0e-20));
return (n_done != 0 ? 0 : 1);
} catch(const std::exception &e) {
std::cerr << e.what();
return -1;
}
}