gistfile1.txt

(define (parse-silence-detect str)
  (define outp
    (regexp-match #px"(silence_start: ([\\d\\.]*))|(silence_end: ([\\d\\.]*) \\| silence_duration: ([\\d\\.]*))" str))
  (if outp
      (map (lambda str
             (let ([strb (list-ref str 0)])
               (if strb (string->number strb) #f)))
           (list (third outp) (fifth outp) (sixth outp)))
      #f))