HDMI wiring and pinout

 Much like USB, HDMI has several different types of plugs and ports.

• Type A is the standard one. A trapezoidal port with two rows of pins, top and bottom, totals 19 pins. It can be found anywhere, from gaming consoles to CCTV servers and TVs.
• Type B, Dual-Link. The same height, but twice the length of type A, hasn't been used in any products.
• Type C, mini HDMI. A scaled-down version of the original port is intended for portable devices like laptops.
• Type-D, micro HDMI. Even a smaller version looks like a mini USB plug. It is used in GoPros and ultra-portable computers the size of a Macbook Air at the time (like the Asus eeePC or various Windows 'ultrabooks').

micro HDMI and mini USB on a GoPro 3+

Every single type of HDMI port (except the dual type B one) has a total of 19 pins. The first eight are for data, and the rest are for power, clocks, and additional functions. That means the most basic functions of video transmission can be carried out by just five pins. MHL, or Mobile HD Link, is a way to wire an HDMI plug to a micro USB. This brings the number of wires to the absolute minimum, with one data lane and one bus for everything else.

Micro-USB to MHL-enabled HDMI, image source: wikipedia.org

Not to bore you with another pin assignment diagram, compare this to the sheer number of functional blocks and lanes in a powerful HDMI transmitter chip.

Functional Block Diagram for Analog Devices ADV7511, image source: analog.com

This brings us to understanding HDMI standards, as they differ not just by the resolution of uncompressed video but by all the additional functions. HDMI has the same confusing cable category naming scheme as USB does with 'High-Speed' and all the way to 'Premium High-Speed with Ethernet'. I don't recommend using those, as looking at just the HDMI standard number is much simpler. The second caveat here should be not to buy any equipment or cables with an HDMI version less than 1.4, as it is already too old and limited.

• HDMI 1.4 is suitable for FullHD video with essential ARC and CEC (in the post on HDMI functions).
• HDMI 2.0 means 4K with some limitations, namely, no 5K or ultra-wide 2160p at 60 fps and no 4K60 with dynamic HDR. HDMI 2.0 has several great functions but are not all available simultaneously.
• HDMI 2.1 spares no expense and provides all the quality imaginable because its bandwidth is three times higher than the one in the previous major version of the standard.

So, what's the difference between cables if they all have the same number of conductors and some plastic covering them? Simple: it's all about materials, meeting the specifications, and having some overhead.

First of all, we should be sure that all the pins are connected to wires. This is neither a joke nor an exaggeration. The right thing to do is to check them with a cable tester. But it is usually easier to check all the additional functions that manufacturers list, then go to Wikipedia and check if all the pairs are used for these functions. If the manufacturer cuts costs or makes a thinner 'easier to work with' cable, it can be a red flag and a sign that fewer wires are used. The HDMI standard specifies video transmission and not all the additional functions, meaning some wires can be absent from the cable.

Then, there's conductor thickness. There is no way to indestructively measure it at home, so the advice is the same: pick a thicker one, as it hopefully represents thicker cores, firmer insulation, and proper shielding. Moreover, in terms of meeting the specification requirements, thicker cable gives more slack to the manufacturer. Wires are typically 28, 26, or 24AWG for different lengths of cables, but this number is not always on the box or the website. Please remember that longer cables should be thicker than shorter ones. By the way, this is exactly the case for buying HDMI over twisted pair extenders. As HDMI cables become longer, thicker, and exponentially more expensive to sustain the same video quality, Ethernet cables could solve this problem.

A good practice is to pick shorter cables, 6 to 10 feet since the percentage of faulty cables is higher in the 10 to 20-foot range. The price difference between high-quality branded and generic OEM 15-foot cables makes it harder for a regular consumer to choose the more excellent option.

Canadian PC enthusiasts at LTT did the tests and discovered that no other gimmicks matter. Specifically, they've proven on a large pool of cables that something seemingly important, like gold-plating the jacks or using silver-plated wires, does not affect the results significantly. A few hundred dollars more for extra-finicky wires does not affect the video quality, just the user's perception.

To sum this all up:

• All the HDMI ports are equally acceptable.
• Thicc and round HDMI cables are more reliable than flat or thin ones. The same goes for the plugs; it's always better to use regular straight connectors than 90-degree-angled ones.
• It's a good rule of thumb to treat HDMI version numbers 1.4, 2.0, and 2.1 as corresponding resolutions: 1080p@60, 4K@30, and 4K@60.
• The more actual HDMI functions listed, the better.
• Try to pick 10-foot cables or shorter from reputable brands.

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Eugenio S