What is the HDMI loop-out function, and why is it different?

Some electronic devices have different names for similar functions. This is based on a broadly understood mix of technical terms and marketing titles. For example, in the early 2000s, everything had to be 'HD', no matter what product you promoted. Then 'HD' and 'Full HD' became less fashionable and more like a technical term for the exact resolution of a display, 1280×720 and 1920×1080 pixels, respectively.

The same thing happens for the HDMI splitter function. It basically is, as the name suggests, splitting the signal from one HDMI input to multiple outputs. As HDMI is not an analog signal, it cannot really be split with a Y-cable. But still, there are a bunch of passive (i.e., those that require no external power supply) splitters out there on Amazon. I'll suggest leaving them for the tiniest field of applications when both (no more than two, really) monitors are extremely close together and the budget for the installation is close to zero. Passive splitters use very little power, as some is provided alongside the digital video signal. But they are very dependent on the cables and their lengths to sustain this load. Funny enough, a cheap and simple splitter requires decent-quality cables to operate, with no guarantee of this kit being reliable. So, I suggest we leave this type of splitter outside our article.

Back to better-designed equipment: active HDMI splitters. Usually, those are small boxes with an external power adapter, used in small installations with a couple of TVs for 24/7 usage in small businesses like nail salons or gyms. Active splitters ensure that if the displays are different, the splitter picks the appropriate resolution and frequency. Active splitters can be used with longer cables, be reliable, and deliver the best possible experience for the viewer.

Moreover, it's splitters job (well, part of it) to help both the source and the display or projector make all the hadshakes. A splitter adds complexity to the connection, so it has to not mess up the HDMI and HDCP connections. A standalone splitter has to support all the EDID signatures and HDCP certificates to establish a proper connection. So, as it often is, the best additional equipment is the absence of it.

This is the reason behind the 'loop-out' function. It represents, in its core, the integration of a splitter into an active extender, switcher, or something of that sort. It is aimed at a very specific use case: local monitoring. This can be useful if we use a smaller display for keeping an eye on the output signal and, in addition, as troubleshooting equipment for the extender itself. Extenders, matrixes, switchers, twisted pairs, and HDMI cables could be finicky, but the first step is to check the source, as it is the input for the extender.

'Loop-out' is common amongst INRIKS devices and can be used in different cases.

Modern Pinterest-inspired gaming setups for small apartments call for a solution like that. This is an entertainment multipurpose machine for Steam and Netflix. The source is usually a PC with more or less tasteful RGB lighting all over it. And then it outputs to two monitors: a regular PC display and a remote TV or projector, usually in front of a couch and a coffee table. Technically, this requires a splitter and a high-quality 4K extender. Using one device instead of two means fewer wires, a cleaner desk, and lower latency. The local monitor is connected to the 'loop-out' HDMI, and the TV uses the extender's in and out ports.

The less obvious use case is professional video production. We are all tired of YouTube reviewers constantly testing any piece of tech they lay their hands on in terms of filming, editing, and rendering video content. But it is indeed a big part of modern-day marketing; professional video equipment is much closer to the everyday office worker than ever before. Streaming live events or hosting webinars is a common thing, and it requires monitoring. On the higher end of the price range, a 7-inch RED monitor will set you back $2600. Cheaper options are not that cheap either. So, if we set up a display in the hallway and a smaller one from Amazon for the cameraman, then that little aux monitor can be hooked up to the 'loop-out' HDMI of an extender.

The next and obvious environment for a loop-out is any lecture hall. From the smallest classroom to the largest theater, a professor needs to see exactly what is shown on the screen behind her or him. The only worse thing than showing something wrong during the lecture is being unaware of it. Most schools need a splitter for the stand, want some simplicity and rigidity, and prefer their equipment to be cheap and easy to replace if broken or lost.

For small businesses, splitting HDMI could be an afterthought. From a salesman's (or that tech-savvy friend's) point of view, when a coffee shop or a nail salon adds a TV, it's easy to say, "Buy an extender for it." It's significantly less easy to then add, "You will need an HDMI splitter box to go along with it." It saves some unnecessary hustle to have such a splitter integrated for the screen near the reception, which used to be hooked up with a cable to some source like a TV box.

To wrap this up, 'loop-out' is a nice thing to have if one needs any type of local monitoring. A simple, exactly 1×2 integrated splitter is a cost-effective way to deal with such cases, adding around 5 to 10 bucks to the price of an extender compared to 20 to 30 for a standalone unit. To my taste, it is just neater, with less cable clutter and no need for an extra socket.

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Eugenio S