HDMI Explained

What is HDMI?

HDMI means High-Definition Multimedia Interface, a standard for simultaneously transmitting digital video and audio from a source, such as a computer or TV cable box, to a computer monitor, TV or projector. Originally developed by a consortium of electronics manufacturers, it has been widely adopted with almost all televisions and computer monitors supporting the interface.

The goal of the HDMI initiative back in 2002 was to improve on existing connectivity standards (e.g. DVI, component video) by creating a smaller connector, adding support for embedded audio and delivering a higher resolution video signal. Such was HDMI's success that by 2008, shipments of HDMI-enabled devices exceeded those of DVI. By the end of 2009, all HDTVs had at least one HDMI port.

HDMI Cables

HDMI Cable Types

4K HDMI cables are sometimes referred to as Premium High Speed and 8K HDMI cables as Ultra High Speed. Premium High Speed HDMI Cable and Ultra High Speed HDMI Cable are trademarks or registered trademarks of HDMI Licensing Administrator, Inc.

HDMI Ports and Connectors

The majority of HDMI connectors in use today are the Type A (Standard), Type C (Mini) and Type D (Micro) shown below. HDMI Type B (Dual Link) was developed for very high-resolution displays but was never used. Also not shown is the HDMI Type E connector which is intended for automotive and industrial applications.

Cables are available in male and female versions, with space-saving right-angled connectors and gripping or locking connectors.

HDMI cable is considered low voltage so you can install it inside a wall. HDMI faceplates give a clean, finished appearance and have a female connector on the internal side, making termination easy. HDMI keystones are also available for digital signage applications and large conference facilities with many displays that are fed from a central location.

Gripping and Locking HDMI Connectors
HDMI connectors do not latch like DisplayPort connectors but some do provide a spring mechanism that makes the blade of a male connector grip the receptacle and makes it less likely that the cable will be accidentally pulled out. If an HDMI device may be subject to vibration or accidental movement, use a connector with a screw lock.

Which is best... in-wall HDMI cable or wireless HDMI?
A cable connection is a relatively inexpensive option that gives a strong, reliable signal but can be difficult to install, it's limited to one location and a distance of 25-50-ft., depending on the resolution. Longer distances require an active cable or HDMI extender. A wireless HDMI extender is much easier to install, can be easily relocated and can broadcast a high-resolution video signal to multiple receivers.
Note: In-wall HDMI cables have a CL2 or CL3 rating. This means that the cable jacket is fire resistant and suitable to low-voltage in-wall applications.

Is there a difference in functionality between the Standard, Mini and Micro HDMI connectors?
All three connectors have the same 19 pins, but some may have different pin assignments. Functionally, they all support the resolutions and features of HDMI 1.4 onwards.

Can a USB-C Port be used to Transmit HDMI to a Monitor?
Yes. In Alt Mode, some of the pins in a USB-C connector are used to transmit other protocols. This allows the widely adopted USB-C port/connector to be used for more than just USB data or power. To date, there are four Alternate Modes: DisplayPort, Mobile High-Definition Link (MHL), Thunderbolt and HDMI. HDMI Alt-Mode supports all of the features of HDMI 1.4b, including video resolutions of 4K @ 30 Hz and above.

I need an HDMI cable for my 4K TV. What should I buy?
Buy a High Speed HDMI cable that supports at least HDMI 1.4, the first HDMI standard to support 4K signals. To get a 4K picture, all components must support 4K: the cable box or streaming service, the HDMI cable and the TV. If you are using an old Standard HDMI cable purchased before 2009, it will not have the bandwidth to carry a 4K HDR signal.

Evolution of the HDMI Standard

HDMI Features

Transition-Minimized Differential Signaling (TMDS) – When digital data is transmitted, especially over long distances, it is susceptible to noise and signal loss. TMDS is a way of encoding an HDMI signal to protect it from interference as it travels from source to receiver. It works like this:

• The sending device encodes the signal, organizing the ones and zeros to reduce the chance that the signal will degrade.
• Two copies of the signal are transmitted over different internal wires, one an "out-of-phase" version of the actual signal.
• The receiving device puts the out-of-phase signal back in phase and compares the two versions, ignoring any differences (noise) between the two.

Consumer Electronic Control (CEC) – This feature allows a user to control up to 15 connected HDMI devices using one remote controller. Most TVs and streaming devices support CEC but it may be turned off by default. Manufacturers sometimes refer to CEC using their own branded term (e.g. Anynet+, Viera Link) so it may not be apparent that your device supports it.

High-Bandwidth Digital Content Protection (HDCP) – this authentication protocol allows a sending and receiving device to verify each other's credentials (stored on each device's Extended Display Identification Data (EDID) chip) and, if every checks out, create a shared key that is used to encode and decode the data passing between them. This process, known as a handshake, happens almost instantaneously at the beginning of a session and ensures that an unauthorized device cannot intercept the data as it travels between two devices. In the United States, HDCP support is mandated by the Federal Communications Commission (FCC).

Display Data Channel (DDC) – The HDMI interface includes support for VESA DDC, a set of protocols that allow a source (a computer's graphics card, for example) to ask a monitor what audio and video formats it can handle, and adjust settings on the monitor, such as brightness and contrast. The information exchanged by a source device and a display is called Extended Display Information Data (EDID) and is transmitted through the Display Data Channel.

Chroma Subsampling – Chroma subsampling is a form of video data compression. It reduces the amount of color data in a video signal in such a way that there is little or no visible impact on image quality.

Each pixel in a video image includes information on brightness (luma) and color (chroma). Since human eyes are more sensitive to differences in brightness than color, chroma subsampling reduces the amount of data transmitted by allowing pixels to share color data with adjacent pixels.

Chroma Subsampling is represented as three digits. The first number is the number of pixels in each row of the sample. The second number indicates the number of pixels in the TOP row that have color information. The third number indicates the number of pixels in the BOTTOM row that have color information.

Color Spaces and Deep Color – A color space is a defined range of colors that can be represented in an image. The two primary color spaces used to represent digital video are RGB and YCbCr. Two important characteristics of a color space are Color Depth and Gamut. Color Depth is the number of bits used to represent the color of a single pixel and determines the amount of shading or gradation. Gamut refers to the number of colors available.

The initial HDMI specification provided support for 24-bit Color Depth (8-bits per color x 3 colors RGB). HDMI 1.3 introduced Deep Color, which added support for 30-bit, 36-bit and 48-bit color depths. It's worth keeping in mind that the human eye can only distinguish around 10 million different color, so 24-bit color is adequate for most situations.

Color Depths

Audio Return Channel (ARC) – Most TVs connect to a sound bar or AV receiver using an optical cable. ARC enables a TV to send audio back to a sound bar or AV receiver through the same cable that delivered the HDMI signal to the TV. In other words, video and audio to the TV and audio back to the sound bar (the "return" part). The benefits of ARC include fewer cables, use of the TV remote to control sound, and the ability to transmit higher resolution audio, such as Dolby TrueHD or DTS HD Master Audio, to your sound bar or receiver. [Version 1.4]

HDMI Ethernet Channel (HEC) –First introduced in the HDMI 1.4b specification, HEC allows Ethernet-enabled devices to share an Internet connection. It combines the features of an Ethernet cable into the HDMI cable, thereby avoiding the need for a separate Ethernet cable. Xbox 360 and Roku are two examples of devices that can take advantage of HEC to connect to the Internet. [Version 1.4]

Dynamic HDR – High Dynamic Range (HDR) is achieved by sending additional information with the video signal that tells the TV or monitor how to display the content. It results in greater brightness, contrast, and better color accuracy as compared to Standard Dynamic Range (SDR). Dynamic HDR simply means the dynamic range can be set on a per-scene basis (or frame-by-frame in the case of high-end TVs).

Enhanced Audio Return Channel (eARC) was introduced in HDMI 2.1 and provides support for higher-quality audio bandwidth and speed. eARC requires a High Speed HDMI cable with Ethernet or an Ultra High Speed HDMI cable. eARC is not backwards compatible with ARC but some products may support both eARC and ARC. [Version 2.1]

Display Stream Compression (DSC) – HDMI is uncompressed audio and video. The higher the resolution, color depth and frame rate, the more bits need to be transmitted until the maximum bandwidth is reached. Then, the only way to transmit more bits is to add more lanes to the cable or compress the signal.

HDMI 2.1 introduced support for Display Stream Compression (DSC) 1.2a, a visually lossless compression for ultra-high definition (UHD) video. Using DSC, an HDMI 2.1 cable can support a maximum compressed bandwidth of 128 Gbps (sufficient for 10K, although it will be some time before there are commercially available devices that need that much bandwidth).

Transmitting HDMI Signals

HDMI Cable Length

Passive Cables – Opinions vary over the maximum length of a passive HDMI cable. Consensus seems to be about 50 feet for 1080p and 25-feet for 4K video, but distances of over 50-feet are achievable. A good practical approach is to try a passive cable and, if you have problems with signal strength, add an in-line signal booster at the receiver end. Tripp Lite Model Number B122-000-4K6 will boost a 4K/60 Hz signal up to 50-ft and B122-000-60 will extend a 1080p/60 Hz signal up to 125-ft.

Active Cables – Length is more definitive in the case of an active cable because signal transmission is designed and tested over the advertised distance. For example, Tripp Lite's P568-065-ACT active HDMI cable will support video transmission up to 65-ft.

HDMI Extenders

When transmission distance requirements exceed the limits of passive and active cables, it's time to consider the various forms of signal extension.

In-Line HDMI Signal Extender – For distances up to 50-feet, an in-line equalizer or repeater can extend a 4K/60 Hz signal up to 50 feet and a 1080p/60 Hz signal up to 125-ft. Greater distances are possible at lower frame rates.

HDMI over Cat5 and Cat6 – A Cat5/6 extender will convert the HDMI signal into similar Ethernet IP packets that can be transmitted over the category cable and reconverted at the other end with no loss of signal strength or fidelity. Using this approach, an HDMI signal can be transmitted about three times further than an active HDMI cable–approximately 100 meters (328 ft.). Shielded (STP) Cat6 cable is recommended for its ability to reduce EMI interference from power lines and crosstalk within the cable.

HDMI over Fiber – The connectors on fiber HDMI convert conventional electrical inputs to pulses of light that are transmitted at high speed through optical fiber, then converted back to electricity on the receiving end. Since signal transmission is optical, it isn't subject to EMI/RFI line noise. HDMI over Fiber can be extended well beyond the 100 meter/328-foot limit of copper Ethernet cable.

Wireless HDMI Extenders – A hardwired extender uses an Ethernet or Active Optical Cable to pass data between a transmitter and receiver. A wireless extender sends the HDMI signal using one of the WiFi protocols (e.g. 802.11ac or 802.11n). Wireless is generally slower than hardwire so make sure the video resolution and frequency is sufficient for your needs. For example, Tripp Lite's B127-1A1-WHD1 can extend a 4K/30 Hz signal up to 98-ft.

Converting To and From HDMI

HDMI and Thunderbolt 3

Can I connect a TB3 port to an HDMI display?
Yes, but not directly. Thunderbolt 3 has native support for DisplayPort and from DP you can get to HDMI by way of an adapter. You can also use an adapter cable like Tripp Lite's U444-006-H4K6BE to convert DP Alt Mode to HDMI.

HDMI to DisplayPort / DisplayPort to HDMI

Can I connect DisplayPort to an HDMI display?
Yes, a DisplayPort to HDMI adapter cable allows you to connect a computer with DisplayPort video output to an HDMI-enabled monitor or TV. If you use a passive cable, make sure the video source is a DP++ (DisplayPort ++) dual-mode port. If your graphics card does not support DP++, use an active cable such as Tripp Lite P582-006-HD-V2A.

Can I connect a DisplayPort monitor to an HDMI port?
Yes. Even though HDMI and DisplayPort use different signal protocols (TMDS vs. LVDS), it is possible to convert HDMI to DisplayPort with no loss of image quality using an active adapter. The adapter may require an external power source. The Tripp Lite P130-06N-DP-V2 4K HDMI to DisplayPort Active Adapter uses power from the USB-A port.

HDMI to DVI

Can I connect an HDMI port to a DVI monitor?
Yes, HDMI and DVI video signals are compatible. An HDMI to DVI adapter will support resolutions up to 1920 x 1200. However, DVI will not support HDMI audio.

HDMI Alt Mode over USB Type-C

USB Alt Mode allows a USB-C connector or port to transmit non-USB signals, making it extremely versatile. For example, a laptop, Chromebook or Android phone might use Alt Mode to directly connect a USB-C port to an HDMI-enabled monitor without the need for an adapter. This is an important feature because many laptops and tablets have a USB-C port but no HDMI port.

To take advantage of HDMI Alt Mode, you need a USB-C port that supports USB Power Delivery. It is the PD handshake that establishes an Alt Mode connection. You will also need a cable with a USB-C connector on one end and a USB-C or HDMI connector on the other. Older USB-A cables do not support Alt Mode.

Another option is to use an adapter cable supporting DisplayPort Alternate Mode, such as Tripp Lite's U444-006-HDR4BE, to connect a USB-C port to an HDMI display.

As a general rule, video and audio can be converted from one protocol to another equal or lesser protocol as the table below shows. Protocol conversion requires an adapter.

Switching and Splitting HDMI Signals

Switches and splitters are often confused and for good reason. They perform similar functions. A switch takes multiple inputs and lets you choose which one to display on your TV or computer monitor. A splitter does exactly the opposite. It takes a single video signal and replicates it to multiple displays.

Can I extend my desktop using an HDMI splitter?
No, an HDMI splitter takes one video signal and replicates it to multiple displays so each display shows the same image. This is known as "mirroring". Here are your options for extending your desktop:

1. If your laptop has an available DisplayPort or Mini DisplayPort port and you want to add an external HDMI monitor, use a DP or mDP to HDMI adapter.
2. If you have a laptop with a USB-C port and want to add an external HDMI monitor, consider a multiport adapter with an HDMI video port.
3. If you have an available USB-C or Thunderbolt port and want to add two or three external monitors, use a dock.

HDMI Surge Protectors

HDMI Audio Extraction

HDMI vs. DisplayPort

HDMI and DisplayPort are similar standards with a different focus. HDMI has been widely adopted by consumer electronics manufacturers. DisplayPort's main focus is computer connectivity and professional audio/video applications.

If you need to connect a Blu-Ray player, cable box, game console or streaming device to your television, HDMI is the logical choice. Your options for connecting a computer monitor to your laptop or desktop PC may be less clear. Many computers (and docking stations) offer both HDMI and DisplayPort. Which one will give you the best results? In terms of image quality, there isn't much difference. DisplayPort 2.0 has a higher bandwidth, allowing it to support higher resolution video, but there are currently few applications requiring video beyond 4K. However, if you need multiple displays, you can daisy-chain three 4K monitors @ 90 Hz or two 8K displays @ 120 Hz.

What's Next for HDMI: 16K Video?

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