daniel,
it is possible to call both keep_codecs_by_name and keep_codecs_by_id, since 101 does not have name:
v=0. o=twinkle 1548176998 229186862 IN IP4 192.98.102.10. s=-. c=IN IP4 192.98.102.10. t=0 0. m=audio 8000 RTP/AVP 99 97 8 0 3 101. a=rtpmap:99 speex/32000. a=rtpmap:97 speex/8000. a=rtpmap:8 PCMA/8000. a=rtpmap:0 PCMU/8000. a=rtpmap:3 GSM/8000. a=rtpmap:101 telephone-event/8000. a=fmtp:101 0-15. a=ptime:20. a=zrtp.
-- juha