The Raspberry Pi 4B is the only SBC that has two HDMI outputs. This makes it especially economical for digital signage. It is capable of simultaneously playing two independent commercial DVD movies on its separate two displays at 1920×1080 each. It also has separate HDMI audio and analog audio devices which can be assigned separately to two video streams.
Alternately program content can be displayed at 3840 x 1080 spread across each two displays per Pi 4B. Content can also be rotated for 1080 x 3840 per Pi 4B. Pi 4Bs can be aggregated for video wall grids of more than 2 displays.
The Raspberry Pi 4B clients have graphic hardware support for H.264 video. By playing on the client instead of a server, network traffic is reduced to close to zero if the content is on the Pi 4B(s), and still greatly reduced if the content is on a cloud compared to playing on a server and forwarding pixels to each of the clients. For telling the clients what to play, another Pi 4B or even a smart phone would be sufficient.
The RaspiPlayer consists of an identical OS on a microSD card for each Pi 4B and of server software to remotely (on same LAN) configure the Pi 4B clients for unique hostnames so that program content can be configured to target each specified display. The configuration/control server communicates with the clients with a unix socket over ssh.
In addition to playing video, it is possible to play a URL including Youtube and to install an app which, for instance, might display time and/or weather, or security or web cams.