An HD video output lets the head unit send video to screens in the back of the car, such as headrest monitors or a fold-down roof screen. Rear passengers can watch a film or a video from a memory stick on a long journey, played from the head unit at the front.
What the video output does
The head unit plays the video and sends the picture out through its video output to one or more rear screens. On many head units the rear screens can show the same video as the front screen, or keep playing while the front screen shows the map or the music. Usually the front controls what plays.
Sound normally comes through the car speakers. Some setups use wireless headphones with the rear screens instead, so passengers can listen without disturbing the driver. Check the rear screens and headphones work together before relying on that.
The connections used
HDMI
An HD video output usually uses HDMI. It carries a digital high-definition picture, often up to 1080p, and can carry sound in the same cable. HDMI gives a sharper picture than older analogue connections, which shows on larger rear screens.
- The head unit's HDMI output is usually a socket or a short lead on the back of the unit.
- Run an HDMI cable through the car to the rear screen, or to a splitter if you want to feed two screens.
- Use a good cable of the right length. Very long HDMI runs can lose signal and may need a better cable or a signal booster.
Analogue video (RCA)
Many head units also have an analogue video output, usually a yellow RCA plug. It carries a standard-definition picture and works with older or simpler headrest screens. The picture is softer than HDMI, but it's simple to wire and reliable over long cable runs.
What the rear screens need
Check the rear screens have a matching input, HDMI or RCA. They also need their own power, usually from an ignition-switched 12V supply so they switch off with the car. Headrest screens are wired through the seat and under the carpet; roof screens through the headlining.
What can and can't be shown while driving
In the UK, a screen showing video, or anything else that isn't information to help with driving, mustn't be visible to the driver while the car is moving. Rear screens are fine for passengers as long as the driver can't see them from the driving seat.
- Rear screens: video is fine for passengers while driving, as long as the screens are out of the driver's line of sight. Headrest screens are well placed for this. Check a roof screen isn't distracting in the rear-view mirror.
- The front screen: navigation, music information, the reversing camera and vehicle information are fine. Video on the front screen is for when you're parked. Many head units block video on the front screen while moving, using the parking brake or speed signal, while still sending it to the rear.
Don't bypass the parking brake or speed signal to show video on the front screen while moving.
Content restrictions
Some streaming apps protect their video and won't send it through HDMI to another screen, so the rear screens go black for those apps. Video from a memory stick and many other video apps usually work. Check the apps you want to use before relying on them for a long trip.
Setting it up
- Connect the rear screens to the head unit's HDMI or video output, and to power.
- Switch on the rear screens and choose the matching input on them.
- In the head unit's settings, turn on the video output and choose whether the rear screens show the same as the front.
- Play a video and check the picture and sound in the back.
Common problems and fixes
No picture on the rear screens
Check each rear screen is set to the right input, and that the output is switched on in the head unit's settings. Try the cable with another screen to rule it out.
The picture shows but some apps go black
Those apps protect their content from being shown on another screen. Use a different source, such as a memory stick.
The picture flickers or drops out
Check the HDMI plugs are firmly seated, and try a shorter or better cable. Route the cable away from power cables.
The front screen goes blank while the rear plays
That's the head unit blocking video for the driver while the car is moving. It's working as intended.
No sound in the back
If the rear screens use their own speakers or headphones, check the head unit is sending sound through HDMI and that the headphones are paired with the right screen.