Today you can have a “home theater”. TVs and video monitors have reached levels of quality and definition that, in the not too distant past, seemed impossible. Collaborating with such sophistication is a technology that brings a lot of practicality: HDMI (or High-Definition Multimedia Interface. For other meanings of HDMI, please see abbreviationfinder).
We are talking about a connector that is present in TVs, monitors, projectors, notebooks and other devices used for displaying videos. HDMI revolutionized the audiovisual market by allowing a single cable to transmit high definition videos and audio.
But how does HDMI work? What resolutions are supported by the technology? What are different versions like HDMI 1.4 and HDMI 2.1 ? That’s what you’ll discover in the next few lines.
What is HDMI?
HDMI is a device connection standard developed specifically for transmitting – combined or not – audio and video content. Behind its development is a team of giants in the electronics industry, such as Sony , Philips , Toshiba and Silicon Image (today, Lattice Semiconductor).
You can use an HDMI port to, for example, connect your notebook to a monitor or to connect different types of devices to your TV: signal receivers, Blu-ray players , video games, digital cameras and so on.
Since the HDMI cable handles both video and audio, it is not necessary to have a specific wire for each thing, as in old standards, such as VGA and DVI.
The HDMI cable connector also has an advantage over previous standards because it is small in size and easy to fit, similar to USB connectors.
At the beginning, HDMI had two types of connectors: HDMI type A and HDMI type B, with 19 and 29 pins, respectively. The type A connector is by far the most implemented in the industry. Type B was never adopted. You will learn more about HDMI cables later in this text.
It doesn’t end there: HDMI technology also offers the advantage of transmitting entirely digitally, allowing you to access excellent quality images in resolutions such as 1080p and 4K.
How HDMI works: the role of the TMDS protocol
One of the main attributes of HDMI is the Transition Minimized Differential Signaling – TMDS protocol. It is important because, although HDMI works with a digital signal, this does not mean that a connection of the type remains free of failures or interference.
TMDS consists of an encoding method that protects the signal from degradation as it passes through the cable. This is done by combining twisted pairs of wires with a digital comparison technique.
It basically works like this: the pair of wires sends the signal, but in one of them, the signal is reversed; the destination device receives the two signals and decodes them so that the signal and its inverse are compared to compensate for detected losses or interference.
When a transmission is initiated, TMDS merges video data (Video Data Period), audio data (Data Island Period) and auxiliary data (Control Period).
Three types of TDMS channels are used in each transmission, therefore. The figure below shows the pins of the HDMI type A connector. Note that each TMDS channel uses two pins. There is also a pair of pins used for the TMDS frequency (TMDS clock), in addition to a shield pin to prevent interference.
| Via | Signal |
| 1 | TMDS Data2 + |
| 2 | TMDS Data2 Shield |
| 3 | TMDS Data2– |
| 4 | TMDS Data1 + |
| 5 | TMDS Data1 Shield |
| 6 | TMDS Data1– |
| 7 | TMDS Data0 + |
| 8 | TMDS Data0 Shield |
| 9 | TMDS Data0– |
| 10 | TMDS Clock + |
| 11 | TMDS Clock Shield |
| 12 | TMDS Clock– |
| 13 | CEC |
| 14 | Reserved |
| 15 | SCL |
| 16 | SDA |
| 17 | DDC / CEC Ground |
| 18 | +5 V Power |
| 19 | Hot Plug Detect |
HDMI Connectors
The HDMI type A connector is so prevalent in the industry that many people think it is the only standard available for the technology. But it is not. Although they are uncommon, we can also find devices with HDMI type C and D ports:
HDMI type A
The HDMI type A connector is by far the most common. It consists of 19 pins and has two bends in the bottom corners to prevent incorrect fitting. It has a standardized size of 13.9 x 4.45 mm.
HDMI type B
The HDMI type B has been developed about the same time that the type A and has the same format as this, only with more pins 25 instead of 19. Also, its size is 21.1 x 4.5 mm.
Its great advantage is having support for a dual link scheme that, as the name implies, doubles the transmission capacity of the connection.
Despite this, the type B connector ended up not being adopted by the industry.
HDMI type C (Mini-HDMI)
Also called Mini-HDMI , HDMI type C , roughly speaking, is a reduced version of type A. The connector also has 19 pins, but its dimensions are more compact (10.42 x 2.42 mm), which makes it suitable for portable devices such as digital cameras and ultra-thin notebooks.
HDMI type D (Micro-HDMI)
The HDMI Type D – Micro-HDMI – can be even more miniature that the HDMI Type C: the connector measuring only 5.83 mm x 2.20 mm, so has size similar to a USB-connector C , for example.
Because it is so compact, HDMI type D is suitable for smartphones or compact digital cameras, for example. Despite its advantages, Micro-HDMI is not very common on the market.
HDMI cables (Standard and High Speed)
HDMI cables are not all the same. You can find versions with different sizes and prices on the market. A single cable should be sufficient for most applications. But there may be devices that work with resolutions that require slightly more sophisticated cables.
There is a standardization of HDMI cables that, although not always followed by manufacturers, helps a lot in choosing the right type. It is the cables that, in the packaging, manual or external part, display one of the following indicators (there may be others, but these are the most common):
- Standard HDMI
- Standard HDMI with Ethernet
- High Speed HDMI
- High Speed HDMI with Ethernet
Basically, Standard HDMI cable is prepared to support resolutions up to 1080i, so options like this tend to be cheap. Eventually, cables of this standard may work at higher resolutions, but there is no guarantee of that.
As you may have guessed, High Speed HDMI cables support higher resolutions, such as full HD (1080p) and even 4K.
Ethernet cables (with Ethernet), on the other hand, are suitable for devices compatible with HDMI Ethernet Channel (HEC), a specification that allows devices connected to a certain equipment to have access to the internet through it. This is the case, for example, of a set-top box that shares the internet with a TV.
Note that you can also find cables with words like Ultra High Speed. Typically, they relate to a category of cabling called 48G , an allusion to the bandwidth of 48 gigabits per second of HDMI 2.1 (you’ll know more about that soon).
In practice, Ultra High Speed cables can handle resolutions like 4K, 5K and even 8K.
If you were confused by these acronyms, access this explanation about 1080i, full HD, 4K, 8K and other resolutions.
From HDMI 1.0 to HDMI 1.3
Just as USB periodically gets new versions (like USB4) and PCI Express gets faster and faster , HDMI is updated over time to bring improvements or new features. These are the first versions:
– HDMI 1.0: launched in December 2002, the first version of HDMI is characterized by using a single cable for video and audio transmission with a data transmission rate of 4.95 Gb / s, a frequency of 165 MHz and support for resolutions such as 1080p at 60 Hz (meaning that 60 frames or frames are displayed per second). HDMI 1.0 works with up to eight audio channels;
– HDMI 1.1: this version basically consists of HDMI 1.0 increased with the DVD-Audio standard. Launched in May 2004;
– HDMI 1.2: this version marked the compatibility of HDMI with screens for PCs (monitors). It also brought support for audio formats such as One Bit Audio , used in media such as SACD (Super Audio CD), in addition to new color schemes. Launched in August 2005;
– HDMI 1.2a: presented in December 2005, this review adopted the Consumer Electronic Control (CEC) specifications – you will know what this is in this text – and specific features for remote control;
– HDMI 1.3: in this version, HDMI now supports frequencies up to 340 MHz, enabling transmissions of up to 10.2 Gb / s and resolutions such as 1920×1080 pixels at 120 Hz and 2560×1440 pixels at 60 Hz. In addition, HDMI 1.3 allows use of a wider range of colors and supports audio standards such as Dolby TrueHD and DTS-HD Master Audio. This version also introduced the HDMI type C connector (mini-HDMI) and eliminated a problem of synchronization between audio and video (lip sync). HDMI 1.3 appeared in June 2006;
– HDMI 1.3a and 1.3b: launched in November 2006 and October 2007, respectively, these revisions brought minor changes to the HDMI 1.3 specifications.
What is HDMI 1.4?
Introduced in 2009, HDMI 1.4 is an update that brought so many advances over previous versions that it ended up being widely adopted by the industry. Here are its main features:
- ability to work with resolutions such as 4096×2160 pixels (as a rule, at 24 Hz), 3840 × 2160 (at 24 Hz to 30 Hz) – these two are considered 4K – and 1920×1080 pixels (at up to 120 Hz – or 120 frames per second);
- transfer rate of up to 10 Gb / s;
- compatibility with a greater number of colors;
- support for the audio return channel (Audio Return Channel – ARC), a subject discussed later;
- possibility of transmission through Ethernet connections up to 100 Mb / s – the aforementioned HEC;
- improved 3D image playback support;
- standardization for vehicle transmission (for car DVD players, for example).
HDMI 1.4 also brought a standardization for cables (the Standard HDMI and High Speed HDMI specifications discussed above) and made the arrival of the also mentioned HDMI type D (micro-HDMI) connector official.
HDMI 1.4a and HDMI 1.4b
Yes, HDMI 1.4 has undergone minor revisions, although they are not very relevant. Announced in March 2010, HDMI 1.4a essentially brought improved support for 3D content. Already the HDMI 1.4b came in October 2011 to bring support for higher resolutions for 3D videos.
The irony here is that, in the end, 3D TVs did not succeed in the market.
HDMI 2.0
The HDMI 2.0 was announced in September 2013 and brings great differential, bandwidth of 18 Gb / s bandwidth (gigabits per second). Thanks to this, support for 4K videos has improved: broadcasts in this resolution and with a frequency of 60 Hz are now compatible by default.
Other attributes include compatibility with up to 32 audio channels, improved support for 3D content, the possibility to broadcast in a 21: 9 screen ratio and the addition of HDMI CEC extensions (learn more below).
HDMI 2.0a and HDMI 2.0b
Presented, respectively, in April 2015 and March 2016, the revisions HDMI 2.0a and HDMI 2.0b brought support for High Dynamic Video (HDR), basically.
HDR is a standard that improves the quality of images by optimizing contrast and displaying more vivid colors, which is why it is increasingly present in TVs and video monitors, for example.
HDMI 2.1: up to 48 Gb / s
It is true that HDMI 2.0 has brought considerable advances compared to previous versions, but it is HDMI 2.1 that promises to make a difference in a market that is increasingly attached to very high resolution images: announced in early 2017, this version works with bandwidth up to 48 Gb / s.
This feature makes HDMI 2.1 capable of transmitting videos in 4K resolution and 120 Hz (remembering, 120 frames or frames per second) or in 8K with 60 Hz. Resolutions such as 5K and 10K are also supported.
HDMI 2.1 arrived as an extension of version 2.0 and, therefore, inherits its features, including support for HDMI CEC and the same types of cables – there were no changes in the connectors.
Other features of HDMI 2.1 include support for eARC (brings compatibility with audio standards with 3D effect, for example; subject covered in this text) and dynamic HDR (when HDR is applied frame by frame), which is the basis for standards such as Dolby Vision and HDR10 +.
What is HDMI CEC?
The HDMI CEC can be so useful that you may have already used this function without knowing its name. CEC stands for Consumer Electronics Control , something like Consumer Electronics Control. The idea is that you can control more than one device using the same remote.
Imagine, for example, that you have a pay-TV receiver connected to your television. With HDMI CEC, you can use the receiver control to decrease the volume of the TV or mute it, for example.
Through HDMI CEC it is also possible to count on the “one touch play” mode. With it, just insert a Blu-ray disc in the player and the TV will activate its HDMI connection and start showing the content, just to give an example; if the TV is off, it will turn itself on.
One-touch playback is interesting for when you have multiple devices connected to the TV: if this feature is in action, you will not need to use the Source button (or equivalent) on the television’s remote control until you find the correct HDMI input.
Note that not all equipment with HDMI supports CEC, so you need to check in the manual or on the product page if this standard is available.
As a rule, HDMI CEC works even between devices from different manufacturers, although exceptions are not rare.
Another important detail: manufacturers can have their own implementation of HDMI CEC and, because of that, name them with another name. Samsung often uses the names Function Anynet and Function Anynet +. LG uses the name SimpLink.
HDCP: to protect content
Many people “wrinkle their noses” when they find out what HDCP means. It is an acronym for High-Bandwidth Digital Copy Protection , a protocol developed by Digital Content Protection with the purpose of preventing illegal capture of content – in other words, fighting piracy.
Its basic operation is like this: the source (sending device, like a video player) communicates with the sink (receiving device, like a TV) through a channel called Display Data Channel (DDC) to know its configuration and obtain an authentication code.
This data is usually stored on a chip called Extended Display Identification Data (EDID). If the code for both devices is compatible, the source obtains a new code and sends it to the sink. The sending and receiving of information from one device to the other is done based on this code.
After that, the code is checked periodically. If an abnormality is found with this procedure, the transmission is interrupted. This can happen, for example, if a third device tries to receive data from the connection.
The industry has implemented this scheme to prevent illegal copying of DVD and Blu-ray content, for example. The problem is that HDCP sometimes blocks legitimate transmissions. This can happen when a device with HDMI is not certified for HDCP or even has, but for an old version of that protocol.
In many cases, the solution to this problem lies in changing the cable or devices used to play the content. Another possibility is the use of an HDCP version converter.
HDMI ARC and HDMI eARC
So far, this text has emphasized the imaging capabilities of HDMI. But this standard is also capable of transmitting high quality audio, as you already know. The problem is that the speakers on most TVs are very simple. It is to overcome this limitation that HDMI ARC comes into play.
ARC stands for Audio Return Channel , in free translation. We are talking about a feature that came up with HDMI 1.4 and allows televisions, video games, TV receivers and other devices to share sound equipment through the HDMI connection.
Imagine you have an Xbox connected to your TV, as well as a soundbar. Thanks to HDMI ARC, the audio from the Xbox will be played on that soundbar instead of being output through the television speakers. If you have also connected a Blu-ray player to the TV, for example, the audio from it will also come out on the soundbar.
To do this, you need to connect the audio device (such as a home theater or a soundbar) to the HDMI ARC port on the TV. If everything is ok, all devices that are connected to the other HDMI connections on the TV will have their audio reproduced by the sound equipment.
The main advantage here is the improved audio experience: HDMI ARC is compatible with high quality audio formats, such as Dolby Digital 5.1 and DTS. It is also possible to adjust the volume of the audio equipment on the TV remote control, for example.
As already mentioned, HDMI 2.1 also brought HDMI eARC (enhanced ARC). This is an improved version of ARC (and backwards compatible with it) that supports even more advanced audio standards, such as Dolby Atmos and DTS: X, which generate sound with 3D effect (as if the audio originated in the environment where you it is). Standards such as Dolby TrueHD and DTS-HD Master Audio are also supported.
What is HML function?
Although it is not a very common practice, it is perfectly possible to connect your smartphone or tablet (and other portable devices) to your TV or monitor via an HDMI connection. One way to do this is by using the MHL function, which stands for Mobile High Definition Link , something like Mobile High Definition Link.
The idea is to allow the connection to be made quickly and without loss of quality. For this, it is necessary to use an MHL cable that basically connects to the smartphone or other mobile device through its USB port (you need to check if it is micro-USB or USB-C) and, at the other end, to the screen via HDMI.
Thanks to the MHL function, it is possible to run a game on the smartphone, but display it on TV or connect a tablet to a video monitor to make it work as a PC (if it has this feature), just to give a few examples.
The most recent version of this technology until the date of publication of this text, the MHL 3, brings compatibility with the previously mentioned CEC function, supports 4K videos, works with 10 W for electrical power (you can recharge your smartphone while it is connected to the TV) and works with high quality audio standards, such as those already mentioned Dolby TrueHD and DTS-HD 7.1.
Note that, to take advantage of the MHL function, you need to make sure that this technology is supported by both your TV (or monitor) and your smartphone (or other mobile device). On older equipment, it may be necessary to purchase an MHL transmitter for the connection to work.
Conclusion
Understanding all the details of HDMI can be difficult, given the amount of technologies and resources associated with this standard for transmitting video and audio via cable.
This guide was written to help you with this task. With it, you can more easily assimilate the HDMI functions that your TV offers or obtain information that will help you buy a monitor, for example. Because of this, it is worth saving this link for future reference.
