[Asterisk-video] H264 video conferencing using Asterisk

[ldac]

    Hi,

I am new in this list and I am almost new using Asterisk. I have 
installed in ubuntu the Asterisk server and I have done an audio 
conference between two PCs (two softphones).

    Now, I would like to add video (h264) but I can not do it. I have 
added to the 'sip.conf' file the 'videosupport=yes' and 'allow=h264'. 
What else should I do from the point of view of the asterisk server?

    Do you think the problem is the client? Have someone done video 
conferencing from one PC to another with an Asterisk server in 
between??? ...

    Any help is welcome and appreciated.
    Thank you very much.
    Regards, LD.

PS: By the way, the voice communication is not as good as I think it 
should be. It is noisy and I suffer some echo. Do I need a high 
performance machine where I have asterisk installed? Or it could be an 
asterisk configuration problem?