Asterisk removed the only media format from OK (for Video) because the media format from the answerer was unknown:
error: VERBOSE[8174] chan_sip.c: Found video description format H264 for ID 99
chan_sip.c: Got unsupported a:fmtp in SDP offer
OK received by * (i took out O and C):
v=0^M
s=-^M
t=0 0^M
m=audio 5000 RTP/AVP 0^M
m=video 5002 RTP/AVP 99^M
a=rtpmap:99 H264/90000^M
a=fmtp:99 packetization-mode=1^M
OK sent by *
v=0^M
s=Asterisk PBX 1.6.1.0^M
b=CT:384^M
t=0 0^M
m=audio 5026 RTP/AVP 0 101^M
a=rtpmap:0 PCMU/8000^M
a=rtpmap:101 telephone-event/8000^M
a=fmtp:101 0-16^M
a=silenceSupp:off - - - -^M
a=ptime:20^M
a=sendrecv^M
m=video 5030 RTP/AVP^M
a=sendrecv^M
This caused the call failed since SDP is not valid (vialate the RFC have at least one media format)
Is this a bug in asterisk?