Keyword Spotting in Speech [closed]

Question

Is anyone aware of a Keyword Spotting System that is freely available, and possibly providing APIs ??

CMU Sphinx 4 and MS Speech API are speech recognition engines, and cannot be used for KWS.

SRI has a keyword spotting system, but no download links, not even for evaluation. (I even couldn't find anywhere a link to contact them for their software)

I found one here but it's a demo and limited.

Answer 1

CMUSphinx implements keyword spotting in pocketsphinx engine, see for details the FAQ entry.

To recognize a single keyphrase you can run decoder in “keyphrase search” mode.

From command line try:

pocketsphinx_continuous -infile file.wav -keyphrase “oh mighty computer” -kws_threshold 1e-20

From the code:

 ps_set_keyphrase(ps, "keyphrase_search", "oh mighty computer");
 ps_set_search(ps, "keyphrase_search);
 ps_start_utt();
 /* process data */

You can also find examples for Python and Android/Java in our sources. Python code looks like this, full example here:

# Process audio chunk by chunk. On keyphrase detected perform action and restart search
decoder = Decoder(config)
decoder.start_utt()
while True:
    buf = stream.read(1024)
    if buf:
         decoder.process_raw(buf, False, False)
    else:
         break
    if decoder.hyp() != None:
        print ([(seg.word, seg.prob, seg.start_frame, seg.end_frame) for seg in decoder.seg()])
        print ("Detected keyphrase, restarting search")
        decoder.end_utt()
        decoder.start_utt()

Threshold must be tuned for every keyphrase on a test data to get the right balance missed detections and false alarms. You can try values like 1e-5 to 1e-50.

For the best accuracy it is better to have keyphrase with 3-4 syllables. Too short phrases are easily confused.

You can also search for multiple keyphrase, create a file keyphrase.list like this:

  oh mighty computer /1e-40/
  hello world /1e-30/
  other_phrase /other_phrase_threshold/

And use it in decoder with -kws configuration option.

  pocketsphinx_continuous -inmic yes -kws keyphrase_list

This feature is not yet implemented in sphinx4 decoder.