I have tested video call but without Audio, ask help

I have did a test video call,we can see each other,but can
hear
nothing,but when I call 600 No,I can hear the voice.ask
help,

error message
{{{
Failed to send voice! timestamp is 0?
}}}
my configure as follow,

Linux OS fedora 6
Asterisk 1.4.13
Iaxclient2.1beta1
video format is Theora
audio format is ulow

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