GStreamer works wonders and combine it with a raspberry pi and you have endless possibilities. This was a hobby project to create a video doorbell which I thought was my million dollar idea until I saw a KickStarter campaign for it (sigh).
Here is a breakdown of what the project required to be done:
1) Video streaming server – on the raspberry pi serving video content, for me this was a live stream from the RPI Camera – I used gstreamer and created a RTSP streaming server in C++.
2) Video streaming client is an android app which receives the stream and display it and processes the push notification from the doorbell press – I used an earlier version gstreamer for android. You can find the full library here: GStreamer for android
3) Basic IO push button hardware – available from sparkfun
4) Python GPIO library to process input from the button – RPI GPIO Library
5) Push notification API (free version) provided by Urban airship – urbanairship
The server starts serving video as soon as the RPI boots up – the button press sends a push notification to the android app – interacting with the notification causes the client to connect to the server and display the video stream.
A video of this in action can be seen at:
Garage Developer's Blog. 
Hi, I’m working on a RPI/Android project (with camera).
I can stream the RPI Camera to Linux computer, but not able to stream it to my Android phone..
Could you give me the Gstreamer config you use at server and client (Android) please ?
Thanks a lot !! š