[[DYNAMIC]] in swf url has nothing to do with the ability to connect and record the stream. you need to append custom AMF data to connect packet with (-C | --conn) switch to successfully connect to the server.
Code:
rtmpdump -r "rtmp://174.122.202.74:443/tinyconf" -a "tinyconf" -W "http://tinychat.com/embed/Tinychat-10.3-1.0.0.0301.swf" -C S:hollywoodempire -C S:none -C S:show -C S:tinychat -C S: -y "122253" --live -o Test.flv
Code:
RTMPDump v2.4 GIT-2011-09-30 (Compiled by KSV)
(c) 2010 Andrej Stepanchuk, Howard Chu, The Flvstreamer Team; license: GPL
Connecting ...
WARNING: HandShake: client signature does not match!
INFO: Connected...
Starting Live Stream
1175.362 kB / 50.24 sec