# How does the player control the display over HDMI?

Two control lines run over the same cable that carries the picture. With them, the player switches the display on and to standby, reclaims its input, and sets its brightness. Whether your display supports this, the device finds out by trying.

> **Type:** concept
> **For:** anyone choosing a display or wanting to know why a switch is missing in the portal
> **Prerequisite:** a display on a device of its own. Display control is included with the **Pro** package and above.
> **Where in the portal:** **Displays** › display › tab **Screen** › **What this display can do**

## Two lines, three abilities

**HDMI-CEC** is the same line a remote control uses to operate a connected playback device. It carries **On and standby** and the command **Reclaim source**. The display switches its input back to the device if someone on site switched to another source.

**DDC/CI** is a data line in the same cable. It also carries **On and standby**, and in addition the **brightness** of the panel.

So both can switch. For the switch in the portal, it makes no difference which of the two paths carries it.

![The player talks to the display over HDMI-CEC and DDC/CI. If brightness is missing, the display software dims by itself.](/docs/devices/bilder/7c9e162e-hdmi-control-lines.svg)

*Both lines are in the same cable and have nothing to do with each other.*

| What | Over which path | Who can usually do it |
|---|---|---|
| **On / standby** | HDMI-CEC | **TVs almost always.** CEC often has to be switched on in the menu first, and every manufacturer calls it something different: Anynet+, Bravia Sync, Simplink, Viera Link. **PC monitors almost never.** |
| **Brightness** | DDC/CI | **PC monitors often.** Usually switchable on and off as “DDC/CI” in the on-screen menu, often off by factory default. **TVs almost never.** |

Commercial displays and panels for continuous operation can often do both, but by no means all of them.

## Why the device asks instead of assuming

Neither the manufacturer nor the model reveals whether CEC is switched on or whether DDC/CI was switched off in the menu, and someone on site can change either at any time. So the device tries and reports only what actually responded.

The result appears in the **What this display can do** card as **Screen on/off** and **Brightness control**, each **available** or **not available**. If an ability is missing, the reason appears next to it, usually **This screen does not expose it**. A switch that has no effect would be the worse answer.

![The “What this display can do” card with the tile for switching the panel on and off (1) and the tile for brightness control (2), and the reason for the missing ability appears below it (3)](/docs/devices/bilder/f199e35b-what-this-display-can-do.png)

*The example shows a web display: Display control is missing there because there is no device with SzeneraOS behind the surface. On a player, the reason names the TV or monitor itself instead.*

## Brightness can always be set

The slider in the **Picture settings** card is always there, but it works in two ways, and the label next to it says which one applies.

| Label | What happens |
|---|---|
| **real brightness** | The display actually dims its panel. This saves power, the picture keeps playing without interruption, and the setting survives a restart. |
| **software dimming** | The display does not expose its brightness. The display software lays a dark veil over the picture. It is less dazzling, but the panel behind it shines unchanged. No power is saved, and with sun on the glass, it may be harder to read. |

## What follows

- **A missing switch is the display’s answer**, not an error in the portal.
- **Patience pays off.** If the display was dark when the device started, it did not respond. The probe repeats by itself, at the latest every 30 minutes. Unplugging the cable and plugging it in again only speeds it up.
- **The cable has to carry the control line.** A very simple cable or a switch in between often does not pass CEC through. Connect it directly.
- **The panel is switched, not the device.** The player keeps running, keeps fetching content, and keeps checking in. Only the surface is dark. That is different from being off air, where the display stays on.
- **This does not work on web displays.** Behind the surface is a browser, not a machine on the cable. There, only the display software itself dims.
- **Almost black is not visible.** If the software dimming is set to five percent or below, the picture is black, even if the panel is switched on. Analytics counts this time as **not visible**, as under a menu of the TV: [What does analytics measure?](/docs/analytics/about-measurement)

## Related

- [Adjust a display’s picture and power](/docs/displays/adjust-picture): orientation, fit, and brightness in the portal.
- [Remote maintenance of a display](/docs/displays/remote-maintenance): **Reclaim source** and the other commands of a surface.
- [Troubleshooting on the device](/docs/devices/troubleshooting): when the switch is set but nothing happens.