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;
  }
}