Snowmix
Video mixer for mixing live and recorded video and audio feeds
... bandwidth links and can work as a standalone CLI based program. Control over both CLI and a TCP connections.
Input and outputs can be done through GStreamer pipelines or the GStreamer shmsrc/shmsink API.
Supported for Ubuntu, Mint, Debian, CentOS, Fedora, Chakra, Mageia, Manjaro,, OpenSUSE and macOS/OS X is supported.
Free support in the discussion forum.
See Snowmix in action on Youtube http://www.youtube.com/user/Snowmix4video