How to create encrypted voice/video communication using SIP and TLS on Android?

I would like to create voice/video communication app on Android using SIP. I know how to setup the SIP acordingly:

http://ift.tt/1iMLmXK

I need the conversation to be encrypted. I figurer using a TLS connection would do the job.

How do I configure SIP to establish a secure connection and communication using TLS on an Android device?