old_contents: class SDP:
      def __init__(self, local_addr, ptime):
          self.local_addr = local_addr
          self.ptime = ptime
  
          local_addr_desc = 'IN IP4 {}'.format(self.local_addr[0])
          self.payload = '\r\n'.join([
              'v=0',
              'o=user1 53655765 2353687637 {local_addr_desc}',
              's=-',
              't=0 0',
              'i=aiortp media stream',
              'm=audio {local_port} RTP/AVP 0 101 13',
              'c={local_addr_desc}',
              'a=rtpmap:0 PCMU/8000/1',
              'a=rtpmap:101 telephone-event/8000',
              'a=fmtp:101 0-15',
              'a=ptime:{ptime}',
              'a=sendrecv',
              '',
          ]).format(local_addr_desc=local_addr_desc,
                    local_port=self.local_addr[1],
                    ptime=self.ptime)
  
      def __str__(self):
          return self.payload
  
new_contents: class SDP:
      def __init__(self, local_addr, ptime):
          self.local_addr = local_addr
          self.ptime = ptime
  
          local_addr_desc = 'IN IP4 {}'.format(self.local_addr[0])
          self.payload = '\r\n'.join([
              'v=0',
              'o=- 6666 2 IN IP4 {local_addr_desc}',
              's=SIP Call',
              'c=IN IP4 {local_addr_desc}',
              't=0 0',
              'm=audio 12100 {local_port} 0 101',
              'a=sendrecv',
              'a=rtpmap:0 PCMU/8000',
              'a=ptime:{ptime}',
              'a=rtpmap:101 telephone-event/8000',
              'a=fmtp:101 0-11,16',
              '',
          ]).format(local_addr_desc=local_addr_desc,
                    local_port=self.local_addr[1],
                    ptime=self.ptime)
  
      def __str__(self):
          return self.payload
  
subject: Update RTP payload