According to the Open Whisper Systems blog the Signal messenger (previously known as TextSecure under Android) now includes support for video calls. To use it, one needs to explicitly enable the beta feature. Of course both ends of a call need to do this.
According to the blog entry, the app uses a lot of the WebRTC infrastructure that was developed to bring real time communications to more applications. I always wondered when I can finally uses a WebRTC based solution instead of the proprietary tools like Skype, Hangouts or others. The "Hello" app contained in Firefox certainly didn't catch on.
Ah and by the way - in case you didn't know - Signal can be used from a desktop system within the Chrome browser. This is very nice alternative for me as I still try to dodge the virtual keyboard on mobile devices as best as I can.