The High-Definition Multimedia Interface, HDMI is an interface that is widely used for audio visual equipment for both domestic and professional application.
When HDMI was first introduced it offered a level of performance that was much greater than that available previously and since then it has developed to accommodate the latest audio and visual standards.
The HDMI interface is used on many audio visual applications from televisions to computer monitors and home entertainment systems to video displays and much more.
The HDMI interface has a far higher specification than previous interconnection systems that were used. As a result HDMI is used for the new High Definition, or HD television systems and Blu-Ray DVD players that are now becoming standard in many countries. The performance of the HDMI interface means that the system is well suited to the very high data rates that now need to be transferred between units within home television, video and theatre systems.
Although there have been many upgrades and developments to the HDMI standard since its initial release they have all retained the original connector, allowing for physical compatibility in addition to the electrical backward compatibility.
The first HDMI standard was launched in 2002 and the first consumer devices using HDMI started to appear in late 2003. HDMI began to appear on consumer HDTVs in 2004 and camcorders and digital still cameras in 2006.
The HDMI standard has a number of key features that are summarised in the table below.
|Salient HDMI Features & Specifications|
|Standard management||HDMI Forum|
|HDMI Forum||7 Founders, 80+ members, 1700+ adopters|
|Connector types||A, B, C, & D
Types A, C, & D 19 pins, Type B 29pins
|Connector measurements|| Width: 13.9 mm (type A), 10.42 mm (type C), 6.4 mm (type D)
Height: 4.45 mm (type A), 2.42 mm (type C), 2.8 mm (type D)
|Video signal||Maximum resolution limited by available bandwidth|
|Audio signal||LPCM, Dolby Digital, DTS, DVD-Audio, Dolby Digital Plus, Dolby TrueHD, DTS-HD High Resolution Audio, DTS-HD Master Audio, MPCM, DSD, DST, Dolby Atmos, DTS:X|
|Max bitrate||Up to 48 Gbps in HDMI 2.1|
|Data protocol||TMDS, Transition-Minimized Differential Signalling|
As technology has developed, so too has HDMI. It has had to accommodate significant changes to video standards with the moves from HDMI being aimed at DVD playback to the latest standard that can accommodate 4K video data transfer for video gaming and other video applications.
The HDMI versions went from a 1 to 2 when control passed from the original HDMI Licensing, LLC to the HDMI Forum, and industry body made up from members with interests in moving the standards forwards.
It is also helpful to have a basic understanding of the different HDMI versions when buying cables and generally checking compatibility and the quality that may be possible from a given system.
A number of HDMI connectors have been defined for use with the HDMI standard. The basic format has not changed over the years making interconnection of devise using HDMI very easy.
There are five types of HDMI connector. These are designated A to E. Of these the Type A is most widely used, and the Type B which can be used for dual link operation has not been incorporated on any products yet.
In addition to this Type C connectors have a mini format, and Type D is a micro format. Type E is used for automotive applications and has an anti-vibration mounting to prevent it becoming disconnected.
HDMI is now a very well established standard and used on most new items of audio visual equipment from televisions to recorders and DVD players and computers to displays and many other items. Being regularly updated the standard will remain relevant for many years to come.