asterisk users - May 2009 - no video by Originate

Hi, all!
i have two ip video phone: 2004,2005,when 2004 directly call 2005,they
both can hear voice and watch video. but if i init call by AMI
command: Originate:
Action: Originate
Channel: SIP/2004
Context: from-internal
Exten: 2005
Priority: 1
...

After,2004 link with 2005,only 2004 can watch 2005's video. but 2005
can only hear voice without video. I am puzzeld. can someone give me
some advise?
my asterisk is 1.4.24