Kaldiio

A pure python module for reading and writing kaldi ark files

• Introduction
  • What is this? What are ark and scp?
  • Features
  • Similar projects
• Install
• Usage
  • ReadHelper
  • WriteHelper
• More low level API

Introduction

What are ark and scp?

kaldiio is an IO utility implemented in pure Python language for several file formats used in kaldi, which are named asark and scp. ark and scp are used in in order to archive some objects defined in Kaldi, typically it is Matrix object of Kaldi.

In this section, we describe the basic concept of ark and scp. More detail about the File-IO in Kaldi-asr: http://kaldi-asr.org/doc/io.html

Basic of File IO in kaldi: Ark and copy-feats

ark is an archive format to save any Kaldi objects. This library mainly support KaldiMatrix/KaldiVector. This ia an example of ark file of KaldiMatrix: ark file

If you have Kaldi, you can convert it to text format as following

# copy-feats <read-specifier> <write-specifier>
copy-feats ark:test.ark ark,t:text.ark

copy-feats is designed to have high affinity with unix command line:

1. ark can be flushed to and from unix pipe.

    cat test.ark | copy-feats ark:- ark,t:- | less # Show the contents in the ark
   

   - indicates standard input stream or output stream.

2. Unix command can be used as read-specifier and wspecifier

    copy-feats ark:'gunzip -c some.ark.gz |' ark:some.ark
   

Scp file

scp is a text file such as,

uttid1 /some/where/feats.ark:123
uttid2 /some/where/feats.ark:156
uttid3 /some/where/feats.ark:245

The first column, uttid1, indicates the utterance id and the second, /some/where/feats.ark:123, is the file path of matrix/vector of kaldi formats. The number after colon is a starting addressof the object of the file.

scp looks very simple format, but has several powerful features.

1. Mutual conversion betweenark and scp

    copy-feats scp:foo.scp ark:foo.ark  # scp -> ark
    copy-feats ark:foo.ark ark,scp:bar.ark,bar.scp  # ark -> ark,scp
   

2. Unix command can be used insead of direct file path

   For example, the following scp file can be also used.

    uttid1 cat /some/where/feats1.mat |
    uttid2 cat /some/where/feats2.mat |
    uttid3 cat /some/where/feats3.mat |
   

wav.scp

wav.scp is a scp to describe wave file paths.

uttid1 /some/path/a.wav
uttid2 /some/path/b.wav
uttid3 /some/path/c.wav

wav.scp is also can be embeded unix command as normal scp file. This is often used for converting file format in kaldi recipes.

uttid1 sph2pipe -f wav /some/path/a.wv1 |
uttid2 sph2pipe -f wav /some/path/b.wv1 |
uttid3 sph2pipe -f wav /some/path/c.wv1 |

Features

Kaldiio supports:

• Read/Write for archive formats: ark, scp
  • Binary/Text - Float/Double Matrix: DM, FM
  • Binary/Text - Float/Double Vector: DV, FV
  • Compressed Matrix for loading: CM, CM2, CM3
  • Compressed Matrix for writing: All compressoin_method are supported: 1,2,3,4,5,6,7
  • Binary/Text for Int-vector, typically used for ali files.
• Read/Write via a pipe: e.g. "ark: cat feats.ark |"
• Read wav.scp / wav.ark
• (New!) Some extended ark format not supported in Kaldi originally.
  • The ark file for numpy, pickle, wav, flac files.

The followings are not supported

• Write in existing scp file
• NNet2/NNet3 egs
• Lattice file

Similar projects

• Python-C++ binding
  • https://github.com/pykaldi/pykaldi
    • Looks great. I recommend pykaldi if you aren't particular about pure python.
  • https://github.com/janchorowski/kaldi-python/
    • Maybe not enough maintained now.
  • https://github.com/t13m/kaldi-readers-for-tensorflow
    • Ark reader for tensorflow
  • https://github.com/csukuangfj/kaldi_native_io
    • Implemented in C++
    • Have interface for Python
    • Support all types of rspecifier and wspecifier
    • Have a uniform interface for writing, sequential reading, and random access reading
    • pip install kaldi_native_io
• Pure Python
  • https://github.com/vesis84/kaldi-io-for-python
    • kaldiio is based on this module, but kaldiio supports more features than it.
  • https://github.com/funcwj/kaldi-python-io
    • Python>=3.6. nnet3-egsis also supported.

Install

pip install kaldiio

Usage

kaldiio doesn't distinguish the API for each kaldi-objects, i.e. Kaldi-Matrix, Kaldi-Vector, not depending on whether it is binary or text, or compressed or not, can be handled by the same API.

ReadHelper

ReadHelper supports sequential accessing for scp or ark. If you need to access randomly, then use kaldiio.load_scp.

• Read matrix-scp

from kaldiio import ReadHelper
with ReadHelper('scp:file.scp') as reader:
    for key, numpy_array in reader:
        ...

• Read gziped ark

from kaldiio import ReadHelper
with ReadHelper('ark: gunzip -c file.ark.gz |') as reader:
    for key, numpy_array in reader:
        ...

# Ali file
with ReadHelper('ark: gunzip -c exp/tri3_ali/ali.*.gz |') as reader:
    for key, numpy_array in reader:
        ...

• Read wav.scp

from kaldiio import ReadHelper
with ReadHelper('scp:wav.scp') as reader:
    for key, (rate, numpy_array) in reader:
        ...

　　　　- v2.11.0: Removed wav option. You can load wav.scp without any addtional argument.

• Read wav.scp with segments

from kaldiio import ReadHelper
with ReadHelper('scp:wav.scp', segments='segments') as reader
    for key, (rate, numpy_array) in reader:
        ...

• Read from stdin

from kaldiio import ReadHelper
with ReadHelper('ark:-') as reader:
    for key, numpy_array in reader:
        ...

WriteHelper

• Write matrices and vectors in a ark with scp

import numpy
from kaldiio import WriteHelper
with WriteHelper('ark,scp:file.ark,file.scp') as writer:
    for i in range(10):
        writer(str(i), numpy.random.randn(10, 10))
        # The following is equivalent
        # writer[str(i)] = numpy.random.randn(10, 10)

• Write in compressed matrix

import numpy
from kaldiio import WriteHelper
with WriteHelper('ark:file.ark', compression_method=2) as writer:
    for i in range(10):
        writer(str(i), numpy.random.randn(10, 10))

• Write matrices in text

import numpy
from kaldiio import WriteHelper
with WriteHelper('ark,t:file.ark') as writer:
    for i in range(10):
        writer(str(i), numpy.random.randn(10, 10))

• Write in gziped ark

import numpy
from kaldiio import WriteHelper
with WriteHelper('ark:| gzip -c > file.ark.gz') as writer:
    for i in range(10):
        writer(str(i), numpy.random.randn(10, 10))

• Write matrice to stdout

import numpy
from kaldiio import WriteHelper
with WriteHelper('ark:-') as writer:
    for i in range(10):
        writer(str(i), numpy.random.randn(10, 10))

• (New!) Extended ark format using numpy, pickle, soundfile

import numpy
from kaldiio import WriteHelper

# NPY ARK
with WriteHelper('ark:-', write_function="numpy") as writer:
    writer("foo", numpy.random.randn(10, 10))

# PICKLE ARK
with WriteHelper('ark:-', write_function="pickle") as writer:
    writer("foo", numpy.random.randn(10, 10))
    
# FLAC ARK
with WriteHelper('ark:-', write_function="soundfile_flac") as writer:
    writer("foo", numpy.random.randn(1000))

Note that soundfile is an optional module and you need to install it to use this feature.

pip install soundfile

More low level API

WriteHelper and ReadHelper are high level wrapper of the following API to support kaldi style arguments.

load_ark

import kaldiio

d = kaldiio.load_ark('a.ark')  # d is a generator object
for key, numpy_array in d:
    ...

# === load_ark can accepts file descriptor, too
with open('a.ark') as fd:
    for key, numpy_array in kaldiio.load_ark(fd):
        ...

# === Use with open_like_kaldi
from kaldiio import open_like_kaldi
with open_like_kaldi('gunzip -c file.ark.gz |', 'r') as f:
    for key, numpy_array in kaldiio.load_ark(fd):
        ...

• load_ark can load both matrices of ark and vectors of ark and also, it can be both text and binary.

load_scp

load_scp creates "lazy dict", i.e. The data are loaded in memory when accessing the element.

import kaldiio

d = kaldiio.load_scp('a.scp')
for key in d:
    numpy_array = d[key]


with open('a.scp') as fd:
    kaldiio.load_scp(fd)

d = kaldiio.load_scp('data/train/wav.scp', segments='data/train/segments')
for key in d:
    rate, numpy_array = d[key]

The object created by load_scp is a dict-like object, thus it has methods of dict.

import kaldiio
d = kaldiio.load_scp('a.scp')
d.keys()
d.items()
d.values()
'uttid' in d
d.get('uttid')

load_scp_sequential (from v2.13.0)

load_scp_sequential creates "generator" as same as load_ark. If you don't need random-accessing for each elements and use it just to iterate for whole data, then this method possibly performs faster than load_scp.

import kaldiio
d = kaldiio.load_scp_sequential('a.scp')
for key, numpy_array in d:
    ...

load_wav_scp

d = kaldiio.load_scp('wav.scp')
for key in d:
    rate, numpy_array = d[key]

# Supporting "segments"
d = kaldiio.load_scp('data/train/wav