import re


def getLength(st):
  """ Searching "content-length" from rtsp strings using regular expressions
  """
  pat=re.compile("Content-Length: \d*")
  pat2=re.compile('\d+')
  mstring=pat.findall(st)[0] # matched string.. "Content-Length: 614"
  num=int(pat2.findall(mstring)[0])
  return num