speech-recognition - アスタリスクの音声認識

Question

http://zaf.github.io/asterisk-speech-recog/

;;Simple speech recognition
exten => 1234,1,Answer()
exten => 1234,n,agi(speech-recog.agi,en-US)
exten => 1234,n,Verbose(1,The text you just said is: ${utterance})
exten => 1234,n,Verbose(1,The probability to be right is: ${confidence})
exten => 1234,n,Hangup()

しかし、次の結果が得られます:-

The text you just said is: -1
The probability to be right is: -1