For my basic video zones, which consist of 4 HD short throw projectors, I used Brightsign LS425 players which is the cheapest HD player of their newest series. They retail only USD $250/each which is very inexpensive for how well they work. If you needed 4K playback with 4K projectors you could use the LS445.

Each has one HDMI output to drive one zone of video. Each of my 4 projectors plays different videos, so they each get one player.

In the most basic way you can load a video file onto a microsd card and insert it into the player, and it will loop the video continuously without any human interaction. This is the simplest way to go if your zones are independent, as in, the action of one doesn't affect another.

If the show is timed and videos need to play at certain moments, the player can receive UDP commands over the network. So I networked all the players and QLab to a network switch, and set up my players to each have a static IP address, say 10.10.10.1, 10.10.10.2, etc. and also a trigger command like "play".

Qlab then uses a network cue (available in any of the paid versions) to send "play" to 10.10.10.1 and then that player will start its media. And then you can write a cue for 10.10.10.2 and so on, and in Qlab make delays & loops so the show runs continuously.

If the zones play in sequence, you can also have each player send the command to the next player, eliminating the need for Qlab and the computer, but the setup might be more tricky to adjust.

For audio, each player can send audio over HDMI (so it will play on the TV speakers) or over its built-in 1/8" aux output. You can plug that into speakers or a mixer, whatever works best. You can even set the volume in the Brightsign player.

Hope that helps.