incorrect time stamp while decoding with chain model

[crpatel]

I have trained chain model using my own data. The model performs correctly with respect to WER. However, the time stamps given by it are not accurate. Time stamps seems accurate at the beginning of audio but start shifting when it approaches towards the end of audio. Our audio files are of length between 2 to 8 minutes. The shift is particularly visible in long files. It seems that the offset in the word time stamp is increasing towards the end of the audio.

My decoding pipeline is as follows:
lattice-push  | lattice-align-words | lattice-to-ctm-conf

Could you please explain why this is happening?

[Jan Trmal]

Use the correct --frame-shift parameter (chain models usually run on factor 3 subsampling of the original audio parametrization rate).

y.

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[crpatel]

I have already multiplied the --frame-shift by 3. The time shift is gradually increasing towards the end of the audio. For example towards the end of the audio, I  can observe the difference of  around 1 second between time shown in ctm and the actual time in audio.

On Tuesday, 27 March 2018 20:07:30 UTC+5:30, Yenda wrote:

Use the correct --frame-shift parameter (chain models usually run on factor 3 subsampling of the original audio parametrization rate).

y.

On Tue, Mar 27, 2018 at 7:12 AM, crpatel <chirag...@gmail.com> wrote:

I have trained chain model using my own data. The model performs correctly with respect to WER. However, the time stamps given by it are not accurate. Time stamps seems accurate at the beginning of audio but start shifting when it approaches towards the end of audio. Our audio files are of length between 2 to 8 minutes. The shift is particularly visible in long files. It seems that the offset in the word time stamp is increasing towards the end of the audio.

My decoding pipeline is as follows:
lattice-push  | lattice-align-words | lattice-to-ctm-conf

Could you please explain why this is happening?

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[Daniel Povey]

Kaldi isn't really designed to operate on such long files.  It would normally be better to break it up into smaller chunks and decode those chunks.

It's hard to diagnose this without knowing more about your decoding pipeline-- e.g. is it using the program online2-nnet3-wav-latgen-faster or an offline decoding setup?  Does lattice-align-words print any warnings?  If offline, check that the number of frames in the file is what you thought it should be based on the duration in seconds.

Dan

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