#Read/write Kaldi features
##Read Kaldi features
###Raw Feature location
Most Kaldi features are stored in mfcc folder with an extension of ark or scp.
####The ark file
The ark stores raw features, its size is normally in few hundred MBs.
Eg: 20 dimensional MFCC features matrix is stored in the ark file like following:
UtteranceID1 [d1 d2 d3 d4 d5 .. d20\n d1 d2 d3 d4 d5 .. d20\n d1 d2 d3 d4 d5 .. d20\n ...]\n
UtteranceID2 [d1 d2 d3 d4 d5 .. d20\n d1 d2 d3 d4 d5 .. d20\n ]\n
Where \n means new line.
To view raw feature, type the following command in the terminal
copy-feats ark:./abc.ark ark,t:
This command means copy the feature from input source (ark:source) to output target (ark,t:target),here we leave "target" empty so the feature will print to the terminal. Following two commands will dump the features to text file
copy-feats ark:./abc.ark ark,t: > a.txt
copy-feats ark:./abc.ark ark,t:a.txt
And dump to binary file:
copy-feats ark:./abc.ark ark:a.bin
####The scp file
It is often saw a scp file which describes the content of an ark file.
The scp is only a text file, with following format:
UtteranceID1 arkLocation1:offset1
UtteranceID2 arkLocation2:offset2
Following two commands will give same results
copy-feats scp:./abc.scp ark,t:
copy-feats ark:./abc.ark ark,t:
####Features in the data folder
feats.scp and vad.scp are two feature descriptors in the Kaldi data folder.
#Write kaldi features
One can write kaldi feature to the ark follow the given text format. However most script in Kaldi require its scp file, one way to create scp file is:
copy-feats ark:./abc.ark ark,scp:b.ark,b.scp