What is HDMI?
HDMI stands for 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.
The HDMI interface allows a port to send high-resolution digital video, theatre-quality sound and device commands through a connector and down a single cable. There are several types of HDMI cable, each designed to support a video resolution and features in the HDMI specification.
HDMI connectors are available in three sizes: standard, mini and micro.
There are also different types of HDMI cable (see the chart below). Not all cables use the logo but the cable specifications should indicate whether it is Standard, High Speed, Premium High Speed or Ultra High Speed. If the type is not indicated, assume Standard.
HDMI Cable Types
|Standard (Category 1)||1080i or 720p||4.95 Gb/s|
|Standard with Ethernet||1080i or 720p, plus a dedicated HDMI Ethernet Channel||4.95 Gb/s|
|High Speed (Category 2)||1080p|
4K @ 30 Hz
|High Speed with Ethernet||1080p or 4K @ 30 Hz, plus a dedicated HDMI Ethernet Channel||10.2 Gb/s|
|Category 3 (4K)||4K @ 60 Hz||18 Gb/s|
|Category 3 (8K)||8K @ 60 Hz|
4K @ 120 Hz
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.
The Standard HDMI connector (Type A) is the most widely used of the five HDMI connector types. These 19-pin connectors can be found on almost every brand of TV, computer monitor, game console, streaming device and desktop computer.
Mini HDMI connectors (Type C) also have 19-pins and support the same features as the full-sized Type A connector in a smaller, more compact form factor. Because of its smaller size, it is typically used on portable devices such as DSLR cameras and tablets.
The smallest HDMI connector, Micro HDMI (Type D), is about half the width of the Mini HDMI connector yet still retains the full functionality of its larger siblings. Micro HDMI connectors are used on small, portable devices such as phones.
Cables are available in male and female versions, with space-saving right-angled connectors and gripping or locking connectors.IP68 HDMI ConnectorPanel Mount HDMI ConnectorRight-Angled HDMI ConnectorLocking and Gripping
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.
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.
Evolution of the HDMI Standard
|Max. Resolution Refresh Rate*||Max. Transmission Rate**||HDR|
|HDMI 1.0||2002||1080p @ 60 Hz||4.95 Gb/s||No||8 audio channels|
|HDMI 1.1/1.2||2005||1440p @ 30 Hz||4.95 Gb/s||No||DVD-Audio, One-Bit Audio|
|HDMI 1.3/1.4||2009||4K @ 60 Hz||10.2 Gb/s||No||ARC, Dolby TrueHD, DTS-HD|
|HDMI 2.0||2013||5K @ 30 Hz||18.0 Gb/s||Yes||HE-AAC, DRA, 32 audio channels|
|HDMI 2.1||2017||8K @ 30 Hz||48.0 Gb/s||Yes||eARC|
* Higher refresh rates are possible using Display Stream Compression (DSC).
** HDMI encodes data and uses some of the available bandwidth to ensure the integrity of the signal. This means that the actual data rate is something less than the maximum transmission rate. For example, under HDMI 2.1, the maximum transmission rate is 48 Gbps but the maximum date rate is 42.6 Gbps.
- Initial release of the HDMI standard
- Audio and video interface for the transfer of video and audio over a single cable
- Data transfer up to 4.95 Gbps
- 1080p at 60 frames per second (UXGA)
- 8-channels of 192kHz/24-bit uncompressed audio (PCM)
- Playback of standard Blu-ray video and audio
- DVD Audio
- Support for YCbCr color space
- Support for low voltages sources, such as PC video cards using PCI Express
- HDMI Standard (Type A) connector for PC applications
- Consumer Electronic Control (CEC)
- Increased bandwidth to 10.2 Gb/s
- Increased color depth to 10-bit, 12-bit, or 16-bit per channel (“Deep Color”)
- xvYCC color space support
- HDMI Mini connector (Type C) for use with portable devices such as camcorders
- Support for Dolby TrueHD and DTS-HD Master Audio formats
- Support for HDMI Ethernet Channel (HEC)
- Support for 3840 x 2160 at 30Hz and 4096 x 2160 at 24Hz
- Audio Return Channel (ARC)
- HDMI Micro connector (Type D) for use with phones
- Increased bandwidth to 18 Gb/s
- 4K at 60 Hz
- 8b/10b signal encoding
- Support for 32 audio channels
- Support for ultra-wide 21:9 cinema aspect ratio
- Increased bandwidth to 48 Gb/s
- Resolutions up to 10K at 120 frames per second
- Dynamic HDR
- Display Stream Compression (DSC) 1.2a
- Enhanced Audio Return Channel (eARC)
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.
- 4:4:4 means no subsampling. Each pixel has its own color information
- 4:2:2 indicates that two adjacent pixels on each row share color information, representing a 50% reduction in color data
- 4:2:0 means the bottom row has no color information and uses the information provided for the top row. This approach reduces the color data by 75%.
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 Depth||Bits per Color||Also Known As||Gamut||HDMI Specification|
|24-Bit Color||8||True Color||16.7 million||1.0|
|30-Bit Color||10||Deep Color||1.073 billion||1.3|
|36-Bit Color||12||68.71 colors|
|48-Bit Color||16||281.5 trillion|
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
Active vs. Passive HDMI Cables
A passive HDMI cable is a simple cable assembly with an HDMI connector at each end. Passive cables have a limited range (more on this later). Active cables on the other hand include a signal booster that enables video and audio to be transmitted over longer distances. Active cables sometimes require a power supply.
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.
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 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.
Blue: Standard cables and no protocol conversion
Green: Adapters and Adapter Cables
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.
An HDMI splitter takes one HDMI video signal and sends it to multiple displays. Each display will show the same image. Splitters are often classified according to their inputs and outputs. For example, a 2-port splitter might be referred to as “1×2” because it has one input and two outputs.
When choosing a splitter, make sure the output is at the resolution and frequency you want. A video splitter may also perform protocol conversion, for example, converting DisplayPort to HDMI.
An HDMI Switch, also called a Presentation Switcher, outputs audio and video from multiple sources but only one at a time. For example, a boardroom presentation might include Powerpoint slides and video from a streaming service like YouTube or Vimeo.
A matrix switch has multiple inputs AND outputs. For example, a 9×2 matrix switch has 9 inputs and 2 outputs.
Another variation on the many-to-one theme is the Multiviewer, which consolidates a number of video inputs on a single monitor. Multiviewers are found in broadcast control rooms and video surveillance systems.
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:
- 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.
- 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.
- 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
A power surge is typically a brief increase in voltage due to, for example, an overloaded circuit, power outage or lightning strike. A surge protector detects excess voltage and safely diverts it through the building’s grounding system so it doesn’t damage connected equipment.
HDMI surge protectors are intended to supplement primary surge protection and are installed “in line” between a video source and display.
Important: surge protectors do not provide two-way protection against power spikes. If you want to protect both source and display, you should install two surge protectors: one with its output facing the video source and one with output facing the display.
Do in-line surge protectors degrade the HDMI signal?
All in-line surge protectors introduce a small impedance into the line and a capacitance across the line. Tripp Lite’s in-line HDMI surge protector (Model Number B110-SP-HDMI) is designed with lower line capacitance and impedance to avoid Transition Minimized Differential Signaling (TMDS) loss.
HDMI Audio Extraction
An HDMI signal includes both video and audio, which is convenient because you need only one cable to connect a cable box, game console or streaming device to your television. But if you want to play audio through an older analog sound system that doesn’t have HDMI support, you will need to separate the audio track from the video. That’s where an audio extractor comes in.
An HDMI Audio Extractor splits an HDMI signal into a separate HDMI signal and an audio output. Depending on the capabilities of the audio extractor, you may have the choice of compressed or uncompressed (LPCM) audio outputs, for example, 3.5mm stereo or a multi-channel format like 7.1 surround sound via TOSLINK.
When buying an audio extractor, make sure the video and audio output formats match the capabilities of your television and sound system.Tripp Lite Model Number
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.
|HDMI 2.1||DisplayPort 2.0|
|Typical Application||Consumer TVs||Computer Monitors|
|Max. Transmission Rate||48 Gbps||77 Gbps|
|Max. Resolution (uncompressed)||4K @ 144 Hz|
5K @ 60 HZ
8K @ 30 HZ
8K @ 120 HZ (DSC*)
|4K @ 240 Hz|
8K @ 120 Hz
16K @ 60 Hz
* Display Stream Compression (DSC)
What’s Next for HDMI: 16K Video?
With 8K TVs and cameras now readily available, first adopters are turning their attention to even higher resolutions, including 10K and 16K, and refresh rates above 60 Hz.
Bandwidth is the biggest barrier to higher resolutions and refresh rates. Ignoring all of the extra data layered on top of the video itself, the simple formula (resolution x refresh rate x color depth) adds up to a lot of bits which need to be moved from a video source to a display. An uncompressed 8K, 24-bit color video signal at 60 Hz needs almost 50 Gbps of data bandwidth.
The current HDMI specification tops out at 8K/120 Hz so a revision will be required to go beyond that.