Riva and k2 ASR WFST decoding (2)

[GNroy]

What does this PR do ?

Adds Riva and k2 WFST decoding options for ASR inference.

Collection: [ASR]

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[github-actions]

This PR is stale because it has been open for 14 days with no activity. Remove stale label or comment or update or this will be closed in 7 days.

[github-actions]

This PR is stale because it has been open for 14 days with no activity. Remove stale label or comment or update or this will be closed in 7 days.

[github-actions]

This PR is stale because it has been open for 14 days with no activity. Remove stale label or comment or update or this will be closed in 7 days.

[artbataev]

Please, make all these dependencies optional
I suggest adding installation to scripts/asr_language_modeling/ngram_lm/install_beamsearch_decoders.sh

[artbataev]

@GNroy, can you please provide the instructions for testing this PR?
A model + test set + LM/text to build LM with the sequence of required operations to build graphs/start decoding (both k2 and Riva).
It may also be worth providing such information for users (make a section in the documentation).

[artbataev]

Please, also fix CodeQL suggestions - most of them seems to be valuable (e.g., 'except' clause does nothing but pass and there is no explanatory comment., This 'lambda' is just a simple wrapper around a callable object. Use that object directly., Variable wfst_path is not used. etc.)

[artbataev]

Should be beam_width=[8]

Otherwise there is an error "no viable alternative at input [8,]"

[GNroy]

Thanks, fixed

[artbataev]

use probs_batch[prob_index].to(device=...)

See warning from PyTorch:

UserWarning: To copy construct from a tensor, it is recommended to use sourceTensor.clone().detach() or sourceTensor.clone().detach().requires_grad_(True), rather than torch.tensor(sourceTensor).

[artbataev]

Please, use f-string when possible (and also print to avoid extra \n).

The following code is significantly more readable:

if preds_output_file:
    print(f'{pred_text}\t{score}', file=out_file)

[titu1994]

That's a stylistic choice, f.write is fine and I prefer it because print does more work under the hood than it needs to. Infact using print is a easy way to mistakenly add newlines without realizing it.

[artbataev]

Looks fine. Thanks.
One suggestion about the decoding_wfst_file with decoding_search_type=k2 (but you can add it after this PR).

[artbataev]

I suggest adding to documentation and here, that decoding_search_type=k2 expects .pt file in decoding_wfst_file. Even if the file was saved by this script (did not exist before calling this script), k2 will fail unless the file ends with .pt.