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