Design Article
HDMI: The digital display link
Bob O'Donnell, IDC
9/4/2007 9:00 PM EDT
Connection History
Until recently, most video-based entertainment devices such as DVD players, set-top boxes, and televisions were limited to analog video connections. To make matters worse, audio connections, even though they moved to digital form several years back, have been separate from video. As a result, achieving a high-quality A/V experience is often a consumer nightmare fraught with multiple, incompatible connection standards, a complicated tangle of expensive add-on cables hidden behind the television set, and a slew of independent devices each with its own remote control. Gone are the days when setting up and watching TV simply meant plugging in a power cord and cable TV signal and using a single remote to turn everything on and off and select channels. Instead, complex interconnections lead to confused consumers and because these connections tend to deliver lower resolution an underutilization of today's high-quality source and display devices. Such factors have thwarted consumers in their quest for a truly fulfilling A/V experience.
The move to digital devices also drove the need for a digital connection standard. The first of these was the DVI (Digital Visual Interface) standard, which made its first appearance on PCs and LCD monitors in 1999 o. DVI is a high-quality digital replacement for the long-standing VGA connector that's been used with PC displays nearly since the first introduction of personal computers. With DVI, which only supports video, PCs and monitors can maintain an all digital-connection between the computer's graphic chips and the display, ensuring an extremely accurate, crisp, readable screen.
When the High-bandwidth Digital Content Protection (HDCP) specification was introduced for DVI in 2000 with the support of numerous content providers, some of the first consumer electronics devices started to offer digital video outputs and inputs. Since the DVI standard was a mature interface technology with industry endorsed content protection, many first-generation HDTV set-top boxes and HDTV-capable TVs began to feature DVI connections. But DVI was limited: the problem of multiple cables for audio and video remained, and DVI brought only limited intelligence to the system. As a result, a group of companies took the DVI framework and began to create a new standard that could carry both digital video and digital audio signals over a single cable and leverage the advantage of a digital connection for other control functions. Their other goal was to create a smaller, more consumer friendly connector. In December of 2002, those goals were realized as the HDMI 1.0 standard and the HDMI connector (see Figure 1).
HDMI Basics
High-Definition Multimedia Interface, or HDMI, is a digital connection standard
designed to provide the highest possible uncompressed video and audio quality over
a thin, easy-to-use cable with a simple, consumer-friendly connector. HDMI can carry
video signals at resolutions up to (and beyond) 1080p in full-color at full 60 Hz (and
higher) refresh rates. It's also backwards compatible with DVI, requiring only a simple
passive adaptor or cable to connect between the two interfaces. Most importantly, it
adds support for up to 8 channels of full-resolution digital audio.all on a single cable.
Since its inception, HDMI has offered the ability to transmit basic control codes from device to device, making the goal of system integration easier to achieve.
HDMI was created as a forward-looking specification with the ability to be updated as further market requirements became apparent. One of the advantages of HDMI is that it is an evolving standard that responds to market conditions and keeps pace with the latest technological innovations. This is a benefit to manufacturers, content providers and consumers in that HDMI continues to enable the highest quality consumer experience. As such, the specification has seen several major enhancements. In version 1.1, support for full definition DVD Audio was added, while version 1.2 offered support for SACD format high-definition audio and a number of enhancements to make the standard easier to use with PCs and PC monitors. Version 1.2a also added a host of new capabilities around the Consumer Electronics Controls (CEC) portion of the specification, which enables the control of multiple devices with a single remote. In June of 2006, version 1.3 was released.
HDMI 1.3: New Capabilities
The most recent version, HDMI 1.3, more than doubles the bandwidth of the signaling
from 4.95Gbps to 10.2Gbps. This increase in bandwidth enables support for even
greater color depths (up to 16-bit per component), higher screen resolutions (1440p
or WQXGA) and faster refresh rates (up to 120 Hz). Additionally, HDMI 1.3 supports
the new xvYCC color space, adds support for the Dolby ' TrueHD and DTS-HD
Master Audio standards, provides a mini-connector for use with portable devices
(camcorders and digital still cameras), and supports the ability to automatically and
accurately adjust the audio to maintain lip-sync with the video image. Table 1
summarizes the capabilities of current and historical versions of HDMI:
The first products employing the HDMI interface were introduced to the market in the fall of 2003 and since then, over 75 million HDMI-equipped devices have shipped into the marketplace. By 2010, IDC expects that just over 1 billion HDMI-enabled TVs, DVD players, PCs, monitors and more devices will be in use in people's homes around the world.
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NickJoh
4/24/2009 3:15 PM EDT
Although an older article it is a good overview of HDMI but focuses entirely on "perceived" advantages overlooking major disadvantages and problems HDMI causes.
The most significant drawback to HDMI is the fact that it is fundamentally for point to point connection of one source to one display.
Many of us have whole house video distribution systems and have become accustomed to watching our TIVO, STB, and DVD outputs simultaneously displayed on all TV's in our homes. It's an incredible convenience that I won't give up but HDMI may mean I will have to live with SD to keep it.
From the article:
BUILT-IN INTELLIGENCE OVER HDMI
HDMI uses bi-directional communication and the increased processing power. . . .
This very bi-directional interactivity thwarts simultaneous viewing on multiple TV's throughout a home.
In a feeble attempt to correct this HDMI now provides for "repeaters" and allows up to 28 displays but this reveals another fundamental flaw in the original "point to point" concept: The EDID!
From the article:
HDMI Intelligence: Automatic Device Configuration.
First and foremost, HDMI uses Extended Display Identification Data (EDID), which is a set of detailed capabilities data for a specific device that is stored in a Read Only Memory (ROM) chip housed inside the device. The EDID ROM contains information such as the display's supported video resolutions, timings and audio capabilities. EDID is always read by the source device upon power up so that the source can quickly and automatically determine which specific format of video and audio signals the attached display can support.
Clearly there was never any thought for supporting multiple displays and the added repeater support accommodating 28 displays is compromised by the single EDID information required for the HDMI source.
That EDID must be the "lowest" video resolution and audio quality of any of the 28 displays. That's right, if you want to drive a 720p kitchen TV with internal stereo speakers through a "repeater" with a source attached to your family room 60" 1080p TV with surround sound all you're going to get on your big TV is 720P and stereo!
And the schemes to overcome this (MoCa, UWB, etc.)require "receiver boxes" at each TV in the $400 range - more than most smaller TV's these days. They also suffer from the least common denominator EDID problem but I suppose more sophisticated devices could present the "highest" common EDID requirement and have the intelligence to reformat the video and audio for the less capable displays. None that do that have been announced and we are in 2009 not 2006 when this article was written. In fact only one company to my knowledge (Gefen) has released a MoCa or UWB solution and they make no mention of supporting more than one "point to point" link so still no "simultaneous" viewing of the same program on multiple TV's.
Now for a comment in my area of expertise:
Do you think HDMI 1.3's "automatic lip-sync correction" feature detects lip-sync error and corrects it? It definitely DOES NOT but that's what the HDMI hype has consumers believing.
This article actually explains what it does pretty well in one place but in another it is highly misleading when it says (about HDMI 1.3):
"and supports the ability to automatically and accurately adjust the audio to maintain lip-sync with the video image."
That is simply not true in the context that most of us would interpret it.
Later in the article:
"This video and audio latency data is included in the display's EDID profile, and can include latency values for both progressive and interlaced video formats. Not only is this HDMI feature precise, but it can be designed to be done automatically and transparently without user interaction."
There you can see that all this feature can do is allow a HDMI 1.3 display to tell a mating HDMI 1.3 A/V receiver to add a fixed audio delay equal to the fixed video delay the display adds.
This will actually aggravate the lip-sync problem when audio arrives delayed which is quite common in DVD's and also happens in broadcasts where their is over correction.
True "automatic lip sync correction" is impossible since there is no watermark in the audio or video to suggest when they were ever in-sync.
The author mentions the feature allows for a different delay to be added for different visual formats having different video latency but in reality those differences may be an order of magnitude less than the lip-sync error variance between arriving programs and DVD's.
The only way to actually correct lip sync is to do it subjectively with a variable audio delay while watching the actual material being corrected. Three companies (Alchemy2, Felston and Primare)make remote controlled digital audio delays for that purpose and HDMI's false claim of "automatic lip-sync correction" hurts those products since most consumers actually believe HDMI - if and when they upgrade their receivers - will correct the problem. It not only won't correct for lip-sync error in the arriving signals but it will actually exacerbate it in many cases.
And my last comment relates to the "absurd" 8 channels of 192 Khz uncompressed audio capability. A double blind study published by the AES proved there is no audible difference in 192 KHz 24 bit audio and 44.1 KHz 16 bit audio. That means HD Audio could just as well have been 8 channels of 44.1 KHz audio. Even that in my opinion would be absurd considering how little information there is on rear channels and how much redundancy there is between all channels. I have no similar credible double blind study to quote but I personally feel such a study would reveal similar findings for any audible differences in 8 uncompressed channels and the long established but older Dolby and DTS compressed audio formats.
That was going to be my last but while I am on this soap box I can't refrain from another elating to the claimed compatibility "advantages" of HDMI.
Nothing has been further from the truth. HDMI 1.1 was an over 300 page spec and it is a moving target now at 1.3. You can't have a 300 page spec and not expect different engineers at different companies to interpret it differently - hence: PROBLEMS.
We've had cases where our customers had to switch from HDMI to component output because they could not defeat their HDMI display's EDID requesting 2 channel PCM (because the TV only has 2 speakers and no Dolby/DTS decoder). The STB took that request via HDMI EDID to mean it should send 2 channel stereo out not only via HDMI audio but also its s/pdif audio outputs destroying any advantage of the customer's surround sound system. Maybe you chalk that up to an error in firmware in the STB but my point is that all this ridiculous complexity in HDMI has created far more problems that it has solved. DVI with a single additional s/pdif cable would have provided (assuming its bandwidth were increased similarly)the same quality video and audio with far fewer problems in my opinion.
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MontyFuller
2/14/2013 9:51 PM EST
Technology transition nowadays is too fast that sometimes it is quite hard to catch up. We are the generation that has witnessed these changes, and the transition frames on the way we consume information, the speed of consuming information, and the quality we require. Gone are the days when products made are dictated by our needs. Nowadays, our escalating needs are realized and dictated by products that continuously plague us each day. Who would think that the iPod would revolutionize the way we treat music? We have never thought of that until we experienced what iPod can deliver. This is the same way that HDMI will soon create some needs in us. We may never realize it, but it will frame on the way we ‘generate’ new kinds of needs, and eventually more and more technology will be created, probably better than HDMI, to answer these new needs. It is like a never-ending cycle. http://www.discountdisplays.co.uk
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