Implementing real time video chat using Android

Does anyone know how to implement voice/video over IP in a android app开发者_开发技巧lication ?

I am trying to understand how it works and should be done. what is the best technology to do that ? is there any good tutorial ?

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check out SipDroid. It does pretty much what you want and is free open source software. You can check out their code and go from there. http://code.google.com/p/sipdroid/