HDMI Explained

HDMI Explained

Standings for according to abbreviationfinder.org, HDMI enables the use of computerized, enhanced or high definition video, as well as multi-channel digital audio on a single cable. It is independent of the various DTV standards such as ATSC, DVB (-T, -S, -C), which are nothing more than data encapsulations of the MPEG format . After being sent to a decoder, the uncompressed video data is obtained, which can be high definition. This data is encoded in TMDS format to be transmitted digitally via HDMI.

HDMI also includes 8 channels of uncompressed digital audio. Starting with version 1.2, HDMI can use up to 8 channels of one-bit audio. 309 bit audio is used on Super audio CDs.

HDMI is one of the words that are most used today when talking about televisions, reproductive equipment and even with computer screens or the same computer equipment. It is beginning to be part of the common vocabulary, as are other acronyms such as USB or FulHD. But what is HDMI really? What is it for? What are the advantages of this connector and cable? It will try to answer these questions and some more in a simple but complete way.

HDMI, which stands for High-Definition Multi-media Interface, is a standard for transmitting uncompressed digital video and audio from one computer to another. It would be the digital version and with copyright protection, of the scart. So with HDMI, you don’t need two cables to connect two computers with that type of connection. A single cable is sufficient to carry HD video (but also standard video) and multi-channel digital audio, as well as signals from the remote control.

Until wireless connectivity arrives, HDMI is postulated as the connection of the future, because not in vain has it been created by industry leaders such as Hitachi, Panasonic, Philips, Sony, Thomson (RCA), Toshiba, Samsung and Silicon Image, in addition to the most important support, the industry of entertainment, such as Fox, Universal, Warner Bros. and Disney.

Connectors and compatibility

Although it may seem otherwise, there is more than one HDMI connector. The most common and used is known, the HDMI class A, with its 19 pins and that can be found in practically all the equipment that has this type of port. However, an HDMI type B with 29 pins has been created and prepared for future displays with much higher resolution than the current one. It is not used at the moment.

More common will become the HDMI type C cable, which would be like the MiniUSB, also designed for portable equipment such as video cameras or photos. It is smaller but still has 19 pins.

The HDMI connector is compatible with DVI equipment and vice versa. This means that we can connect an HDMI source to a device with a DVI connection or a device with DVI to a display with an HDMI input. An adapter is required. Of course, you will only get an image. So the sound and signal from the remote control is lost.

If you have been looking at HDMI cables, you are sure to find a big price difference between one and the other. In general, it can be said that any of them work under normal conditions and without having long cables in operation. Like other signals, HDMI loses with distance.

To clarify this issue a bit, LLC incorporated with the HDMI 1.3 specification. two categories of cables:

  • Standard or category 1, which are those cables that reach 75 Mhz.
  • High speed or category two, for those cables that reach 340 Mhz, the highest bandwidth available today.


In addition to uncompressed video and audio, the HDMI connection is capable of sending information from the remote control. This translates into something magical: being able to control multiple devices with a single remote control if they are connected via HDMI. This is called HDMI CEC (Consumer Electronics Control), and most new equipment is already supported.

Of course, you have to be careful because each manufacturer calls this feature with a different name, which sometimes leads to errors. Sony for example calls it Bravia Sync Theater, Samsung has named it Anynet +, Panasonic calls it Bravia Link or EZsync, LG has christened it SimpLinkand Pioneer has not been complicated: HDMI Control.

The operation of the HDMI CEC is not complicated: the system, usually the screen, identifies the elements that are connected via HDMI, configures them appropriately and starts to control them with a single button or remote, yours. Virtually all manufacturers are embracing this functionality in their multimedia equipment for the living room.

HDMI versions

Since in December of 2002 the HDMI 1.0 standard was established, several updates have been up to the present, the HDMI 1.3. You may have heard about the 1.3a and 1.3b specification, but for the consumer they are not important.

This HDMI 1.3 standard. introduced at the end of 2010 a series of improvements, among which the increased bandwidth to 340 MHz (10.2 Gbit / s), support for Dolby TrueHD, DTS-HD, TrueHD and DTS-HD sound and the introduction of the HDMI Type-C connector for notebook computers.

The higher versions of the HDMI standard are fully compatible with the previous ones, although at the moment it is not possible to update to higher versions of the HDMI standard, since the current updates require both Hardware and Firmware modifications. The only equipment prepared for this type of update is the Playstation 3 console, since it already had the necessary hardware elements. In fact, it was the first team to use HDMI 1.3.

HDMI 1.0 (December 2002). Single digital audio / video connection cable with a maximum bitrate of 4.9 Gbit / s. Support up to 165Mpixels / s in video mode (1080p60 Hz or UXGA) and 8-channel / 192 kHz / 24-bit audio.

HDMI 1.2 (August 2005). Support for One Bit Audio, used in Super Audio CD’s, up to 8 channels is added in this specification. HDMI Type A availability for PC connectors.

HDMI 1.3 (June 2006). The bandwidth is increased to 340 MHz (10.2 Gbit / s) and support for Dolby TrueHD and DTS-HD is added. TrueHD and DTS-HD are low loss audio formats used on HD-DVD and Blu-ray Disc. This specification also has a new minijack format for camcorders.

HDMI 1.4

It is a cable through which it is possible to send not only high definition video and audio, but also data and 3D video. HDMI 1.4. It also kicks off an improvement in resolution that we now call FullHD. This new specification is capable of sending video with resolutions up to 4096 × 2160 at 24 fps or 3840 × 2160 at 30 fps and is known with XHD.

The new specification also introduces enhancements to extended color support, allowing the new HDMI to bring truer colors to a TV, especially when a video camera is connected.

The audio also undergoes improvements. There is now an audio return channel which will require fewer cables to have a surround sound system connected to the television.

A curiosity that HDMI 1.4 brings is the advance to be able to see high definition video in motion. The new specification is concerned with maintaining quality despite vibrations or noise. It is thought directly in high definition in cars and public transport.

One of the most interesting new features that the HDMI 1.4 specification introduces is the ability to send and receive data through an Ethernet connection built into the cable itself with speeds of up to 100 Mbps.

This step forward is of vital importance today, because both televisions and reproductive equipment are assuming Internet connectivity as something logical and are incorporating an Ethernet port or even WiFi connectivity. In a computer with HDMI 1.4 we would not need that extra Ethernet connection, because with the same cable we would be bringing the video, sound and Internet connection to the television anywhere.

Advantages and disadvantages

Since we do not need more than one cable to send, uncompressed, video and audio from one computer to another, the advantage of this connection is clear for the consumer. In addition, as we have seen with the HDMI CEC, the use of the equipment is greatly simplified. And it is a bidirectional connection, which makes self-configuration and easy control a fact, as we can say that the different computers are capable not only of receiving information but also of sending it at the same time and communicating with each other. And let’s not forget the quality it offers us.

In the case of the industry, the main advantage is the control they have over copyright thanks to HDCP.

Regarding the inconveniences, in addition to those derived from the control of the signal, we have that at the moment the port and the connection between equipment is very susceptible to accidental disconnections, since the cable is not anchored to the equipment but simply connected.


The standard HDMI Type A connector has 19 pins. A higher resolution version -type B- has also been defined, but its use has not yet become widespread. Type B has 29 pins, allowing an expanded video channel to be carried for high resolution displays. The latter was designed for higher resolutions than 1080p, that is, larger image size.

HDMI Type A is backward compatible with a DVI single link, used by modern computer monitors and graphics cards. This means that a DVI source can be connected to an HDMI monitor, or vice versa, via a suitable adapter or cable, but the audio and HDMI remote control features will not be available. Furthermore, without the use of HDCP, video quality and resolution could be artificially degraded by the signal source to prevent the end user from viewing or mostly copying protected content. HDMI Type B is similarly backward compatible with a trial DVI link.

Connector details

Example connector: Molex 500254-1907

Pin assignment of a type A connector
Pin Signal mapping Pin Signal mapping
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 +
eleven TMDS Clock Shield 12 TMDS Clock–
13 CEC 14 Reserved
fifteen SCL 16 SDA
17 DDC / CEC ground 18 + 5V Power
19 Detection of “hot” connection (Hot Plug)

Technical specifications

TMDS Channel

  • It carries audio, video and auxiliary data.
  • Signaling method: according to DVI 1.0 specifications, single link (HDMI type A) or double link (HDMI type B).
  • Video pixel frequency: 25 MHz to 165 MHz (type A) or 330 MHz (type B). Video formats below 25MHz (ex: 13.5MHz for 480i / NTSC) are transmitted using a pixel repeat scheme. Up to 24 bits per pixel can be transmitted, regardless of frequency.
  • Pixel encoding: RGB 4: 4: 4, YCbCr 4: 2: 2, YCbCr 4: 4: 4.
  • Audio sampling frequencies: 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96kHz, 176.4 kHz, 192 kHz.
  • Audio channels: up to 8.