[Asterisk-video] I have tested video call but without Audio, who can help me?

[db peng]

I have did a test video call(by Iax),we can see each other,but can hear
 nothing,but when I call 600 No,I can hear the voice.who can help me?
 my configure as follow,

 Asterisk 1.4.13
 Iaxclient2.1beta1
 video format is Theora
 audio format is ulow