I have a network video stream (mjpeg) from an android phone that acts as an ip webcam and I would like to use it as an actual webcam on my pc (for google talk, skype etc.)
What you might use is an application that puts the ip input on a video4linux device:
I use droidcam (http://www.dev47apps.com/). Install the droidcam app on android (free version should suffice) and the client on your ubuntu machine. Go to the folder in which you extracted the droidcam tar bal (tar.gz).
Run it :
It does all the work for you. The only thing you should provide is the (local) ip adress of your android device.
Test it using vlc:
To let skype use the v42l device:
This is what i do, but there might be other ways to convert to have an ip stream convert as a video device which can be displayed by skype,etc.