Published on 24th Jan, 2018 by Cable Chick

HDMI CEC ARC & Ethernet Simplified

HDMI CEC ARC & Ethernet Simplified


HDMI CEC ARC & Ethernet Simplified

HDMI may be best known for Full HD and 4K video capabilities, but today we're going to look at some of the lesser-known features which are often used as selling points, but are frequently misunderstood.

The World of Acronyms

HDMI you may already know as High Definition Multimedia Interface. This encompasses the hardware, the cable, its plugs, the video stream it carries, and its extra features all in one name.

CEC stands for Consumer Electronics Control, and is the digital implementation of an old SCART protocol called AV.link. It allows connected AV devices to talk to and control each other. HDMI has extended this functionality to perform more operations on more devices.

ARC is the Audio Return Channel. One or two wires inside a HDMI cable may be used for sending a secondary audio stream back to a source or hub device such as a home theatre receiver or soundbar.

HEC is the HDMI Ethernet Channel, and enables HDMI connected devices to access the internet without each of them requiring separate Ethernet cables. Because HEC and ARC use the same two wires inside the HDMI cable, the names are sometimes combined to HEAC - HDMI Ethernet Audio Channel - for brevity.

The HDMI Ethernet Myth

HDMI with Ethernet Logo

The technical specification for HEC allows for a 100BASE-TX 'Fast Ethernet' connection up to 100 Mbit/s for data transfer and could, in theory, provide easier access to firmware updates or even streaming video services. In reality, HEC is rarely implemented in this way (if at all), especially on consumer level home theatre equipment. In most circumstances, internet access is provided for by a WiFi chip or dedicated Ethernet socket and HEC simply isn't used.

For example, your Smart TV can already stream Netflix or YouTube (via its built-in apps) by directly connecting to your existing home internet network. This avoids the trouble of having to ensure all your devices and cables are HEC-ready, or for the TV manufacturer to put extra hardware inside the TV to act as the gatekeeper other devices' network access. While it may seem handy if BD-Live and game console multiplayer could be handled though a single cable, these devices would always prefer a dedicated link for the best speeds and cheap, proven internal hardware.

When shopping for home theatre devices, don't let any promises about HDMI Ethernet abilities sway your purchasing decision - its very likely to go unused in your home!

ARC - a One-Trick Pony

ARC's main benefit is enabling multichannel audio from digital television and streaming apps on your Smart TV to make it back to your home theatre receiver so that your favourite shows can use more than just the built-in TV speakers. By using HDMI ARC, you don't have to run a separate cable (such as SPDIF Toslink) to your amp. The best audio this type of ARC link allows for is compressed 5.1 (if the source offers it) which suits most broadcasts these days.

HDMI ARC with compressed 5.1 surround ability

The big limitation is when attempting to use ARC to pass-through audio from another source device. For example, if you connect a Blu-ray player directly to your TV, it may use an ARC link to your home theatre receiver to pass along the audio stream. Unfortunately this pass-through signal is often restricted to stereo only! Solving this problem means running that extra SPDIF cable anyway.

HDMI ARC pass-through with limited stereo ability

Different TV manufacturers implement their own choice of ARC capabilities depending on how strictly they adhere to the HDMI requirements, but you can't bet on 5.1 being available for pass-through links on every model from any particular brand, and you're not likely to find that information in the user manual, either!

Getting the Best Out of ARC

HDMI ARC is exceptionally helpful for Smart-TV apps like Netflix, or broadcast TV channels. It can also be helpful in a pinch for simple pass-through audio on stereo sources like old consoles. In many cases, ARC can be skipped in favour of an SPDIF output if your TV supports it - digital coaxial or Toslink cables are fairly cheap and have no pass-through limitation.

ARC socket on a home theatre receiver
ARC on a receiver

In order to enjoy the maximum uncompressed multi-channel audio stream from a Blu-ray or similar source, it will need a direct HDMI connection to your home theatre receiver, leaving ARC to only provide a link for audio coming out of the TV's own apps and antenna connection.

HDMI v2.1 and eARC

HDMI v2.1 was announced in late 2017 and includes specification for a new Enhanced Audio Return Channel (eARC) protocol which will allow better multi-channel audio support for formats like Dolby Atmos and DTS-X. However, this may not solve the problem of HDMI's restriction of stereo for pass-through signals, so even HDMI v2.1 television sets may not work as hubs if you want the best possible audio.

The Many Names of CEC

Each device manufacturer has their own trade name (or several) that refers to their own set of CEC abilities and inter-operabilities. Here's a short list of the most common brands and their special names for HDMI-CEC:

AOC: E-link LG: SimpLink Panasonic: VIERA Link / EZ-Sync
Philips: Fun-Link Pioneer: Kuro Link Samsung: Anynet+
Sharp: Aquos Link Sony: BRAVIA Link / BRAVIA Sync Toshiba: CE-Link / Tegza Link

Apart from confusion on the spec sheet when comparing brands, these trade names can also hide incompatibilities between devices from different manufacturers, so a home theatre network that isn't brand exclusive may not communicate over CEC as intended for all operations!

What CEC Can Do

Remote Control Clutter
Simply your home theatre with CEC

In simple terms, CEC enables devices connected via HDMI to communicate simple commands and statuses to make automation of a home theatre easy. In many ways, well-implemented CEC commands could eliminate the need for multiple remote controls on a basic home theatre set-up.

Most of the time, CEC will allow for operations such as auto-on, auto-off and system volume control. Other features such as one-touch recording, device menu control and even remote control pass-through are likely to cause issues unless all your devices are the same brand. Learning which functions are available for your specific home theatre is a matter of try-it-and-see, as information on command compatibility isn't available between brands.

Generally, you can expect your TV remote control's volume adjustment to operate the amplifier, and the channel change buttons to operate your STB or satellite receiver, etc. Inputs and output are also auto-selected or powered-on via CEC when certain related events take place, and turning the TV off should put all active devices into stand-by as well. These basic automations reduce remote swapping frequency, and may eliminate some remotes altogether.

Practical CEC Uses

Brand-Exclusive Home Theatres

If your home theatre is brand exclusive and doesn't include any third-party or non-CEC devices like the Xbox One, you may be able to program an existing remote to operate all the connected devices, allowing 'universal' control out of the box. This task is made easier because your user manuals will detail the CEC abilities and configuration under their brands' trade names so you can follow along to get started easily.

Mixed-brand Home Theatres

Enabling all the different CEC protocols on a mixed-brand system can still offer simple automation. For example, if you grab a PS4 controller and wake up your console, the TV can switch to the corresponding input and maybe switch your receiver over, too. Likewise, if you use your TV remote to select the Blu-ray input, the Blu-ray can be instructed to power-on and become available automatically. In this instance, you'll still need all your remote controls, but you may not need to pick them up as often.

As mentioned earlier, what you'll get and how well it will behave can change for every different mix of brands and devices - but it doesn't hurt to try it out.

Universal Remote Controls

If your home theatre is driving you crazy with CEC incompatibilities or limitations, your best bet for total home theatre automation is to disable CEC altogether and invest in a universal remote. Even simple remotes like the Logitech Harmony 650 can replace all of your home theatre remotes and provide one-touch reconfiguration of your inputs and outputs. Fancier universal remote controls have more granular access to functions and can make operating a home theatre foolproof for non-tech savvy users.

Unfortunately a rare few TV brands (we're looking at you, Hisense) don't work perfectly with third-party remotes and may always need the original remote handy for some operations.

CEC Technical Talk

CEC is very slow. 400 to 500 bit/s is all manufacturers get for device control, and commands run about 15 bytes total. This limit doesn't look to have been changed in the HDMI 2.1 specification, so CEC isn't likely to have a lot of time spent on refinement in the future. There's also a 15-device limit for CEC networks, and its implementation on devices is entirely optional.

CEC also comes in several versions, with v1.4 being the most widely used because it offers manufacturers greater control (and can be used to force brand loyalty to access the best features). CEC v2.0 has been around since 2013 and is considered a better, stricter standard, but its easier for manufacturers to keep using their existing systems so change is slow.

CEC can also be defeated by intermediary devices such as HDMI switches, splitters and matrixes. Even those which state they are CEC compliant may hinder the passage of commands. Again, it is nearly impossible to know in advance if a particular intermediary device will cause a problem in an existing setup as CEC is such a dog's breakfast in terms of implementation.

The Final Verdict

HDMI Ethernet is a non-starter for home theatre equipment and it's not likely to change in the future. It can be disregarded as a useful feature on hardware, but when purchasing cables you may as well go with HEC compatible options as ARC will use the same pinouts.

HDMI ARC is the easiest way to get the best audio from Smart-TV apps and free-to-air broadcasts. If both your surround sound receiver (or soundbar) and TV have ARC sockets, use them. However, if you use your TV as a hub for other source devices like Blu-ray players, you're going to be better off using the TV's SPDIF link to get the best pass-through audio as well. Remember, ARC audio quality is limited to the same compressed 5.1 you'll get from SPDIF anyway.

HDMI CEC is a very handy feature to enable on your home theatre devices, especially if all your tech is the same brand. If you've not tried it before, enabling CEC is easy, and can always be reversed if it doesn't behave the way you think it should. Simple commands are almost always supported between brands, and it can be very handy in reducing the amount of remote swapping you do each day.

Probably the best news about these three HDMI features is that they're all non-essential and have back-up options readily available that can usually outperform the originals.

Questions?

Is all this technical talk giving you a headache? Contact us with any questions you have about HDMI and we'll do our best to simplify them!