In the past we spun our own solution which involved converting vga to standard def video and capturing that. We wrote custom scripts involving gstreamer and vlc, to Mix video from networked ptz camera and laptop video converted to standard def. Then streamed that to youtube live. We are currently converting to hdmi capture(for laptop video) and OBS studio for mixing, capture and streaming. I would recommend something along those lines as OBS studio is opensource and is the defacto standard for twitch/youtube live streamers.  Which means there is now a market for hdmi capture devices priced for consumers.

socallinuxexpo github has much of are work, we will be better at getting our next gen stuff for next year up there.