code: def pack_remb_fci(bitrate, ssrcs):
      
      data = b'REMB'
      exponent = 0
      mantissa = bitrate
      while mantissa > 0x3ffff:
          mantissa >>= 1
          exponent += 1
      data += pack('!BBH',
                   len(ssrcs),
                   (exponent << 2) | (mantissa >> 16),
                   (mantissa & 0xffff))
      for ssrc in ssrcs:
          data += pack('!L', ssrc)
      return data
docs: Pack the FCI for a Receiver Estimated Maximum Bitrate report.
  
      https://tools.ietf.org/html/draft-alvestrand-rmcat-remb-03