I have a project that requires something like a video conference call between an android (and Iphone) phone and another device running android, a raspberry pi 3 in which android can be installed. There's no internet involved but the two devices have wifi
I have a very old app that does this – sends pseudo-video and audio between two devices. My app is based on Erel's tutorial, I believe the CCTV example, from long ago.
It uses network sockets, async streams, and the video is camera preview bitmaps sent at about 10 fps.
I wanted to send true video, but as Erel says that is very difficult. The app could probably be updated, but it works fine for its intended purpose.
Barry.