My Swann security cameras work well, but they can only be viewed with proprietary apps -- a major shortcoming in today's voice-enabled smart home. I finally found a work-around. Maybe this will help someone else facing the same limitations. I spent about $20 for an HDMI-to-RCA converter and an RF modulator. Luckily, I had extra cable runs in the walls already.
The network video recorder (NVR) is in the basement and supports two monitors. The TV is wall mounted with HDMI and Component cables going to a nearby wall plate in the family room. The signal path is:
NVR Monitor 2 port --> HDMI cable --> RCA converter (=composite video)
--> RCA cable --> RF modulator (=RF video on channel 3)
--> coax cable to family room component video wall plate
--> RCA cable from wall plate to TV "antenna" jack (with adapters)
I repurposed one of the existing component cables by...
adding a screw-on male phono plug to the coax
adding a male coax F adapter to the other end of the chosen component cable
moving the chosen cable to the TV's "Antenna" jack
I show and hide the camera window using the TV's picture-in-picture function, commanded through Alexa, implemented via IR signals through a Harmony hub.
I expected a poor quality image after all of the video conversions, but was pleasantly surprised. The design is slightly embarrassing, but it works! (Our family room has a lot of windows, so I took the photo from below to remove glare. Thus, the unusual viewing angle.)