H264 packetization with echo app

25 Aug 2011

      Hey Guys,

I have recently started playing with the echo application for video
calls and found some possible issue (asking here if this is the
desired behavior).

Scenario:
 * Call gets connected with echo application, echoing audio just fine.

 * On reinvite the client sends the following SDP(please note the line
with a=fmtp:102 packetization-mode=1):
{{{
v=0.
o=dan.test 0 1 IN IP4 10.10.10.106.
s=-.
c=IN IP4 10.10.10.106.
t=0 0.
m=audio 48576 RTP/AVP 9 96 97 0 8 98 100 5 6 15 101.
a=rtpmap:9 G722/8000.
a=rtpmap:96 speex/32000.
a=rtpmap:97 speex/16000.
a=rtpmap:0 PCMU/8000.
a=rtpmap:8 PCMA/8000.
a=rtpmap:98 iLBC/8000.
a=rtpmap:100 speex/8000.
a=rtpmap:5 DVI4/8000.
a=rtpmap:6 DVI4/16000.
a=rtpmap:15 G728/8000.
a=rtpmap:101 telephone-event/8000.
a=extmap:1 urn:ietf:params:rtp-hdrext:csrc-audio-level.
m=video 55774 RTP/AVP 102 99.
a=rtpmap:102 H264/90000.
a=fmtp:102 packetization-mode=1.
a=imageattr:102 send [x=[0-640],y=[0-480]] recv *.
a=rtpmap:99 H264/90000.
a=imageattr:99 send [x=[0-640],y=[0-480]] recv *.
a=nortpproxy:yes.
}}}

 * FreeSWITCH accepts it with 200 OK, returning the following SDP:
{{{
v=0.
o=Webi 1314226434 1314226435 IN IP4 10.10.10.106.
s=Webi.
c=IN IP4 127.0.0.1.
t=0 0.
m=audio 32256 RTP/AVP 9 101.
a=rtpmap:9 G722/8000.
a=rtpmap:101 telephone-event/8000.
a=fmtp:101 0-16.
a=silenceSupp:off - - - -.
a=ptime:20.
m=video 18750 RTP/AVP 102.
a=rtpmap:102 H264/90000.
}}}

Issue as seen by me:
FreeSWITCH remaps the 102 from an offer with packetization=1 to a
reply with packetization information missing, therefore defaulting to
0 (default out of RFC).

Question:
* Is this intentional or just some wrong negotiation of packetization
parameter? Is FreeSWITCH not supporting packetization=1?

Based on the negotiated stream the client should send now 102 with
packetization=0 (as preferred by FreeSWITCH in signaling) and
FreeSWITCH should return to the client 99 since 102 with
packetization=1 does not look like being supported.

My FreeSWITCH version is the latest git compiled yesterday:
{{{
/opt/freeswitch/bin/freeswitch -version
FreeSWITCH version: 1.0.head (git-8f15bc7 2011-08-23 14-40-44 -0500)
}}}

Thx in advance for any tip!

DanB

Dan-Cristian Bogos

Anthony Minessale

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