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HDMI Part 1 - A Digital Interface Solution

HDMIThere is a lot to talk about HDMI for one article, so I will cover the subject in 10 articles each addressing a different area of HDMI. This first article is about specs and versions. A special request made by Shane Sturgeon, our Magazine Chief Technologist & Co-Publisher, gave me the idea of covering other areas of HDMI not well covered by the press that often prompt Magazine readers to ask for help on the Tips list and the Forum.


HDMI, What is it for you?


Many people talk about HDMI as a cable, or as a spec, or as a chip, as a simplification of digital connectivity, as the end of HD content protected viewing for 10 million early adopters of HDTVs with only component analog connections, as a de-facto standard adopted by hundreds of manufacturers, as a connection that sometimes causes more problems than it resolves, etc. Well, it is all of the above; and depending on a person's agenda, he/she might be very unyielding about some of that list and entirely ignoring the others.


HDMI, How was it created?


Silicon ImageOn December 9, 2002, the seven founders of HDMI (High-Definition Multimedia Interface) announced the 1.0 specification of this connectivity standard, the enhanced, more robust form of DVI (see below). The seven founders are Hitachi, Matsushita, Philips, Silicon Image, Sony, Thomson, and Toshiba.

The standard supports HD uncompressed video, 8-channel digital audio (reportedly up to 192 KHz), and some control signals, all on a single cable (15 mm, 19 pin), while using less than half the available bandwidth of HDMI. HDMI was created with the same video capacity as DVI, or up to five Gbps of bandwidth, double what a HD signal would require, and is backward compatible with DVI by using an adapter, although that is for the video part only since DVI does not handle audio. With the newest version of HDMI announced in June of 2006, HDMI has doubled its bandwidth capacity to 10.2 Gbps.

HDMI is quickly replacing DVI and is being implemented already on many products, and is becoming the de-facto standard for transporting uncompressed signals over a cable.


HDCP (High-bandwidth Digital Content Protection)


This article is not intended to cover the details of HDCP.

The HDCP 1.0 specification was developed by Intel with contributions from Silicon Image in February 2000 to protect DVI outputs from being copied by providing a secure link between a video source and a display device.

HDCP offers authentication, encryption, and renewability. The Motion Picture Association of America (MPAA) endorsed HDCP as the standard for the secure transmission of HD signals over DVI, and is used on HDMI as well.


A Quick Summary of the Ancestor (DVI)


The DVI (Digital Visual Interface) 1.0 specification was introduced in April 1999 by the Digital Display Working Group integrated by Silicon Image, Intel, Compaq, Fujitsu, Hewlett-Packard, IBM and NEC for the purpose of creating an digital connection interface between a PC and a display device. It is a connection with enough bandwidth for uncompressed HD video signals.

The 1.0 DVI specification is a point-to-point solution that supports video content but not audio, HDMI does. DVI uses the Transition-Minimized Differential Signaling (TMDS) protocol developed by Silicon Image. PanelLink is the Silicon Image's proprietary implementation of TMDS.

More background and specifications can be found on a Digital Connectivity Tutorial I wrote for this Magazine at:

http://www.hdtvmagazine.com/articles/2006/04/digital-connectivity-a-tutorial.php

This tutorial is also included as a separate section on every Yearly HDTV Technology Report, also found on this Magazine at:

http://www.hdtvmagazine.com/reports/hdtv-technology-review.php


Do we need HDMI?


Maybe our need for simplified cabling is not as much as the motivation of the Motion Pictures Association of America (MPAA) to protect their content, but today's digital world is increasingly in demand for more efficient and secured ways of accessing, distributing, and managing digital content any time any where; and HDMI has become the connection of choice by the HDTV industry for our living rooms.

Component analog and Firewire connections have their place as well.

Component analog was used as the only HD video connection on the first 5 years of HDTV adoption (1998-2003), the problem is that it is unprotected, and for that reason content providers preferred DVI or HDMI as a more secured method to transport an HD signal from a source equipment to a display device (TV, projector, panel).

IEEE1394 Firewire, also covered in the Digital Connectivity Tutorial, is being used for transporting HD compressed signals in digital form for a network or for recording devices, such as D-VHS and external DVRs. Firewire was implemented using a form of content protection called DTCP (also called 5c, for the five companies that found the standard).

One could efficiently record a compressed HD video signal with a bandwidth of 19.4 Mbps transported over Firewire, but it would not be practical to try to record its uncompressed form with approximately 2.2 Gbps of bandwidth, and even if someone wants to try that, DVI or HDMI with HDCP content protection would not allow it.

How could it take 2.2Gbps? The 1080i HD format has 1125 total lines of 2200 pixels x frame (active image 1080x1920), there are 30 frames per second on 1080i, requiring 74.25 MHz/pixels (1125 x 2200 x 30fps). Each pixel contains data for RGB and is implemented by DVI/HDMI with 30 bits (8 per each color plus another 6 for encoding). A 1080i HD 74.25 MHz/pixel signal would require 2.2 Gbps speed rate. Try to transport a 1080p/60fps signal and it could double up that bandwidth requirement.

Many modern HDTVs have the 3 types of connections for backward compatibility and for the different purposes they support, but there are still many earlier generation HDTV sets on the consumer hands (about 10 million) that could be resold as used equipment that only has component analog connections, or could still be used on other rooms of the house.

Beware; it could happen that a protected program running over such unprotected analog connection would not be able to be viewed as HD, even when you pay for the rightful viewing of the content (as PPV, VOD, or premium channel). I cover this subject in depth on this article:

http://www.hdtvmagazine.com/articles/2006/02/analysis-of-dtv-content-protection-rulings-and-agreements.php

So hello HDMI, the path seems inevitable, for now.

HDMI has been able to transport the maximum HD quality of 1080p since day one in an uncompressed manner, the digital storage capacity required by a 2hr movie at 1080p quality is by itself overwhelming even to today's storage dreamers, and with the added HDCP content protection protocol (courtesy of Intel) HDMI/HDCP is considered very secured.

However, nothing could be absolutely secured anymore in the world, it is a matter of time and human will, many protection methods might be broken eventually. With the rapid advances of high capacity storage facilities, storing uncompressed HD video could one day be as cost effective as storing a CD is today, and some day a teenager in a corner of the world might claim that even HDCP could be circumvented.

He would then write the instructions of how to do it on the bottom of his skateboard, or publish it on the web as it happened already with DVD and other cases. Morals and human intelligence when used for a negative purpose are always in a constant clash to live in harmony, and HDMI/HDCP could be challenged as well.


HDMI version 1.3, the Excuses


People are talking about version 1.2 and version 1.3 and why they prefer to wait to get blah-blah features. Version 1.3 has been officially out for a few weeks already, the availability of chips and audio/video equipment using those chips is another story, it could take months, some say equipment could be using 1.3 chips by Christmas, Sony's PS3 expected by November claims it would have it.

I recently received an invitation from Leslie Chard, President of HDMI Licensing LLC, upon their introduction of version 1.3 in June of this year. Leslie had the courtesy to give me a private presentation before the official release to the press; the information below was taken from the presentation.

I also used the opportunity to exchange ideas about several subjects regarding HDMI, including some issues people are having when using HDMI, which took away some of the glowing image of HDMI, some with merit some without.

There are some rumors running about version 1.3 as the only one linked to 1080p, and that earlier versions would not be 1080p capable. One should not condone a manufacturer that installed a non-1080p HDMI chip regardless of the version into a $39 DVD player that just needs to output 480i/p, why? It does not have any use for the 1080p capability.

However, what is not right to some 1080p interested consumers is that equipment that claims 1080p handling capability be suited with a non-1080p HDMI chip that bottlenecks such ability.

In some cases, the TV might actually have the 1080p capable HDMI chip but might not have the proper TV design to internally handle 1080p between the chip and the final display of the image. Many first generation 1080p HDTVs recently introduced do not accept 1080p due to these reasons; cost decisions, market choices, etc. not the HDMI spec, any version.

It is unfair to HDMI that many manufacturers were blaming the unavailability of the HDMI 1.3 spec for their inability to accept 1080p on their 1080p TV sets, when actually even the version 1.0 spec was capable to handle such resolution, obviously the proper chip was not installed.

A similar situation could be mentioned for the incorrect claims that without HDMI 1.3 a new Hi-def DVD player (of either format) could not output new multichannel lossless audio formats (Dolby True-HD, DTS-HD, etc) to an A/V receiver.

Actually it could, the player converts the new audio format as LPCM and send it to the A/V receiver that way even thru a non-1.3 HDMI connector. For that to happen, the player must have the proper audio decoder for the lossless audio format read from the disc. Version 1.3 would permit the encoded audio to be streamed out as is read from the disc, for an external decoder to do the job (future A/V Receivers); there are some pros and cons on doing this. This subject is covered in depth in the following article:

http://www.hdtvmagazine.com/articles/2006/04/multichannel-audio-for-hd.php


The Versions


Let us start with some basic bullets about the HDMI specs on each version:

HDMI 1.0 (Dec 2002)
-Max Video Performance
1080p @ 60Hz refresh rate, or UXGA (PC format)
24 bit RGB/36 bit YCrCb color depth

-Max Audio Performance
8 channels uncompressed digital audio @ 192kHz, 24 bits per sample
Support for all existing Dolby & DTS compressed formats

Time Line:

December 2002June 2004August 2005December 2005
HDMI 1.0HDMI 1.1HDMI 1.2HDMI 1.2a
Initial specificationAdded support for DVD-AudioAdded support for SACDCEC Functionality fully specified
 Improvements to compatibility testingPermits use of RGB color space for monitor applicationsTesting required for specific cable lengths
  Supports low-voltage (AC-coupled sources) in PCsCertified Connector List -required to pass ATC testing

1.3 Next Gen HDMI Performance
-Maximum bandwidth increased from 165 MHz (4.95Gbps) to 340 MHz (10.2Gbps)

-Technical foundation established for future bandwidth increases

-Support for increased refresh rate and next generation displays
e.g. 1080p @ 60Hz with 36 bit RGB, or 1080p @ 90Hz refresh rate WQXGA displays (1440p)

-Added support for Deep Color for increased color bit-depth 30-, 36-, and 48-bit RGB/YCbCr

-Current 24 bit color enables ~17 million colors. Deep color enables billions of colors. Helps eliminate on-screen effects such as color banding

-Added support for next generation "xvYCC" color standard, will allow the display of any viewable color (1.8X as many colors as existing standard)

-Version 1.3 ensures highest possible signal resolutions from next generation video sources: Blu-Ray and HD-DVD, PS3, HDMI-equipped PCs

-Maximum Audio Performance
Version 1.3 adds support for future Dolby TrueHD & DTS-HD Master audio formats (Blu-ray/HD-DVD). Lossless compression formats bring a similar digital surround experience as original theater movies.

-Automatic Lip Sync timing compensation to enable automatic correction for most common audio/video sync issues

-Mini connector for camcorders, digital-still cameras, etc.


The latest HDMI specification can be downloaded at no cost by visiting www.hdmi.org


Stay tuned for Part 2, coming soon to a HDTV theater near you, the HDTV Magazine.

Posted by Rodolfo La Maestra, July 25, 2006 9:57 PM

About Rodolfo La Maestra

Rodolfo La Maestra is the Senior Technical Director of UHDTV Magazine and HDTV Magazine and participated in the HDTV vision since the late 1980's. In the late 1990's, he began tracking and reviewing HDTV consumer equipment, and authored the annual HDTV Technology Review report, tutorials, and educative articles for HDTV Magazine, DVDetc and HDTVetc  magazines, Veritas et Visus Newsletter, Display Search, and served as technical consultant/editor for the "Reference Guide" and the "HDTV Glossary of Terms" for HDTVetc and HDTV Magazines.  In 2004, he began recording a weekly HDTV technology program for MD Cable television, which by 2006 reached the rating of second most viewed.

Rodolfo's background encompasses Electronic Engineering, Computer Science, and Audio and Video Electronics, with over 4,700 hours of professional training, a BS in Computer and Information Systems, and thirty+ professional and post-graduate certifications, some from MIT, American, and George Washington Universities.  Rodolfo was also Computer Science professor in five institutions between 1966-1973 in Argentina, regarding IBM, Burroughs, and Honeywell mainframe computers.  After 38 years of computer systems career, Rodolfo retired in 2003 as Chief of Systems Development from the Inter-American Development Bank directing sixty+ software-development computer professionals, supporting member countries in north/central/south America.

In parallel, from 1998 he helped the public with his other career of audio/video electronics, which started with hi-end audio in the early 60’s and merged with Home Theater video, multichannel audio
, HD, 3D and UHDTV. When HDTV started airing in November 1998, and later followed by 3DTV and 4K UHDTV, he realized that the technology as implemented would overwhelm consumers due to its complexity, and it certainly does even today, and launched his mission of educating and helping consumers understand the complexity, the challenge, and the beauty of the technology pursuing better sound and image, so the public learn to appreciate it not just as another television.