HDMI-CEC for digital signage: switch screens on and off without a remote

CEC is a single shared wire in every HDMI cable, separate from the video signal. Devices on it send short messages to each other: "standby", "I am the active source", "power status?". The wiring is mandatory in HDMI, but a device does not have to implement CEC, which is why it works on one TV and not the next (Wikipedia).

Two messages matter for a sign:

• One Touch Play (image view on). The player says it is the active source, and the TV turns on and switches to its input.
• System Standby. The player tells the TV to go to standby.

TV makers rename CEC in their menus. If you cannot find "CEC", look for the brand's name (Wikipedia):

Turn it on in the TV's settings, usually under General, External devices, or HDMI.

Most "CEC is broken" reports come down to one of these:

1. It is off on the TV. Many TVs ship with it off, and a factory reset or firmware update can turn it off again.
2. Something sits in the middle. HDMI switches, splitters, extenders and AV receivers commonly block or rewrite CEC. Plug the player straight into the TV.
3. The TV ignores wake-up in deep standby. Some TVs drop CEC in their lowest power mode. Look for a quick-start or network-standby setting, and test a full overnight cycle before you trust it.
4. Another device grabs the TV. A soundbar, console or second player on the same TV can send its own CEC commands and switch the input away.
5. The player cannot send CEC. Many streaming sticks and Android boxes do not let an app send CEC commands at all.

The only real test is to schedule an off and an on, leave it overnight and look at it in the morning, or ask your agent for a screenshot and the power the player reports.

On screenRIG every Player declares the display power methods it can use, and your agent reads them before it acts. From the Player guide:

An on-screen blackout is not CEC: the screen goes black but the panel stays powered. It still hides the content out of hours, and it works on every Player.

The Player reports the power it actually achieved, so you can tell "the TV is off" from "we asked the TV to turn off".

A display schedule lists up to 16 windows when the display is on, in the screen's timezone. Outside every window the display goes to standby. The Player evaluates the schedule on the device, so it keeps working offline. Ask your agent in a sentence, or set it with the CLI:

{"enabled": true, "windows": [{"days": ["mon", "tue", "wed", "thu", "fri"], "start": "07:00", "end": "19:00"}, {"days": ["sat"]}]}

screenrig screen display-schedule set --tag Cafe --file hours.json

For a one-off, such as a late event, screen display overrides the schedule until its next boundary or for a set time:

screenrig screen display --tag Lobby --power on --for 3h

The CLI reference covers display schedules, overrides and the health each Player reports.

Turning a screen off is half of it. The other half is getting a stuck screen back without a ladder. A Player that declares the capability can be told to:

• Reboot the device, on Raspberry Pi and Linux kiosk installs, BrightSign, Windows and managed Android. A reboot sent to an offline screen waits, queued, for up to 24 hours and runs when the screen comes back.
• Restart the Player app without rebooting the device.
• Clear its cache, keeping its pairing and settings, and download its content again.

Scheduled reboots, such as every night at 04:00 in the screen's timezone, come with every plan. You also hear about trouble without watching a dashboard: every project starts with an email to its owner when a screen has been offline for 10 minutes, and notifications can watch for a disconnected display, a device running hot, a Player that keeps crashing, or a screen showing a blank or frozen picture.

Should HDMI-CEC be on or off for digital signage?

On, if your player can use it and you want the screen switched off out of hours. Turn it off if another device on the same TV keeps switching inputs or waking the screen.

Is HDMI ARC the same as HDMI-CEC?

No. ARC (Audio Return Channel) sends sound from the TV back to a soundbar or receiver. CEC sends control commands. They often sit in the same menu, and a soundbar on ARC usually takes its volume commands over CEC, but they are different features.

How do I tell if my TV has HDMI-CEC?

Look in the TV's settings for CEC or the brand's name for it (the table above). If the menu has it, the TV implements CEC. Then test it with your player before you mount the screen.

Can an Amazon Signage Stick turn the TV off?

With screenRIG, the Amazon Signage Stick blacks out the picture on a schedule that runs on the device, even offline. That is not a CEC command, so the panel stays powered. Use a Raspberry Pi, a Linux PC or a BrightSign player when you need the TV itself switched off.

• en.wikipedia.org/wiki/Consumer_Electronics_Control
• screenrig.ai/docs/players
• screenrig.ai/docs/cli