Use WebRTC (Web Real time Communication)

it's a free, open project that provides browsers and mobile applications with Real-Time Communications (RTC) capabilities via simple APIs. The WebRTC components have been optimized to best serve this purpose.

Here's an android app sample using it.

https://github.com/RWebRTC/WebRTC-Android-Learn

And this is the official webRTC website: https://webrtc.org