The Secret Life of HDMI - Part 3
Last week we looked at the data rates used by video over the HDMI connection. That gave us a good idea of just how fast even basic video data can move along an HDMI cable. We also mentioned that the HDMI interface was designed to be flexible so that extra features could be added over time.
This week we start to look at the various versions of HDMI that have appeared over its history. At first it seems like a key consideration when considering an equipment purchase ought to be “does it have the latest version of HDMI?” However, not all features of a HDMI version are implemented on every product offering that version of the interface.
The right choice of equipment depends on many factors and the planned use of HDMI is one of them. When looking for a new piece of equipment it’s always worth thinking about which features you really need (or are likely to use in the future). While some of these might be HDMI related, some non-HDMI features might be of a higher priority and be important for the device being a pleasing long-term purchase.
From the outset the HDMI interface offered some key advantages over the connections that had gone before. While DVI was a good choice for digital HD video it was difficult to find DVI equipment that also supported audio over the DVI connection. Installers also dislike the form factor of the DVI connector as it’s relatively large and the side thumbwheels make running cables through walls a difficult exercise.
The smaller HDMI connector makes installation easier and, even at the outset, offered a good combination of key features…
Digital Video – up to 1980 x 1080 pixels progressive (1080p)
Digital Audio – either 2 channel (stereo) up to 24-bit 48kHz PCM or Bitstreams (Dolby Digital, DTS etc.)
Copyright Protection – HDCP (High Definition Content Protection)
EDID – Device identification to automatically establish capabilities etc.
While V1.0 of the interface offered lots to excite both installers and consumers it wasn’t long before the flexible nature of HDMI allowed the addition of extra features. At V1.1 HDMI gained:
Multichannel Digital Audio – up to 8 channels of up to 24-bit 192kHz PCM audio
This addition was important to support the (then) upcoming DVD-Audio format. Although this type of disc later fell from favour the ability to receive 8 channels of very high resolution audio was useful when new, higher definition surround sound formats appeared on BluRay and HD-DVD players.
Where V1.1 had been a fairly modest update, V1.2 added a larger gamut of features. These included:
Wider Colour Space – support for the wider RGB colour space used on PCs
PC resolutions – support for extra video resolutions used by computer monitors
One bit Audio – the ability to transmit one bit audio streams such as those from SACD discs
As you can already see the development of HDMI has been frequent and has added some important features. Next week we continue the story with V1.2a and V1.3, perhaps the biggest update released so far.