video call implementation in android
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