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Chris Llana, Editor


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Some Thoughts on HDMI (Or, do you want 1080p and Dolby TrueHD?)

April 2, 2006 (slight updates 4/4 and 4/7)

HDMI. High-definition Multimedia Interface. It's digital. It's what gets the video and audio signals from your new high-definition DVD player to your new high-definition TV, without degradation and without compromising those signals' security.

In other words, HDMI is not just another pretty electrical cable. In concert with the HDCP (High-bandwidth Digital Content Protection) protocol, it provides a high-bandwidth encryption-decryption system connecting the components in your home theater. It's certainly not just a cable.

It's also used in other applications, like computers and other consumer electronics, but we'll stick to TVs here.

So why do you need to know about it, other than to plug the cable in? Well--

All HDMI interconnects are not created equal. The new ones can do a lot more than the older ones, so if you want to see and hear the latest best sound and video, you need to pay attention to your interconnects.

Blu-ray Disc and HD-DVD

I decided to look into this HDMI business after reading several conflicting articles about certain alleged limitations of the new HD-DVD and Blu-ray Disc players. Depending on the source, the players either would or wouldn't pass through 1080p video (the seeming defacto standard for high-definition movies) or the new ultra-high fidelity audio standards (DTS-HD Master Audio, Dolby TrueHD, Dolby Digital Plus).

Some articles said some of the players themselves weren't up to snuff; others said it was the HDMI interface. What I found was that the HDMI standard (like most everything else in digital TV) is in a state of transition. Becoming more capable.

The current HDMI standard is 1.2 (announced August 23, 2005). The much-improved version 1.3 is expected to be released by the middle of 2006.

By the way, Silicon Image, Inc. is the entity responsible for licensing HDMI products (via HDMI Licensing, LLC). The HDMI Specification is developed by Silicon Images and Sony, Hitachi, Thomson (RCA), Philips, Matsushita (Panasonic), and Toshiba.

The new improved version 1.3 is expected to include (taken from a January 3, 2006 press release):

  • Higher speed: Though HDMI has more than twice the bandwidth needed to support all HDTV formats, HDMI will increase its single-link bandwidth to support the demands of future HD display devices, such as higher resolutions, deep color and high frame rates.
  • Deep color: HDMI will support 30-bit, 36-bit and 48-bit color depths for stunning rendering of over one billion colors in unprecedented detail.
  • Greater PC/CE convergence: HDMI will be enhanced for easier integration into low voltage, AC-coupled PC graphics controllers, cementing HDMI's position as the de facto standard digital multimedia interface enabling true convergence across PC and CE platforms. The HDMI Founders also support compatibility between HDMI and the Unified Display Interface (UDI), the HDMI-compatible digital video interface for PC displays announced recently by a group of leading PC technology makers.
  • New mini connector: With small portable devices such as HD camcorders and still cameras demanding seamless HDTV connectivity, HDMI will offer a new, smaller form-factor connector option. Since HDMI offers the highest quality digital audio and video on a single connection, such devices will be also benefit from a reduced connector count.
  • Lip Sync: CE devices are employing increasingly complex digital signal processing of high-resolution video and audio formats to enhance the clarity and detail of the content. As a result, synchronization of video and audio in user devices has become a greater challenge and could potentially require complex end-user adjustments. HDMI will incorporate features to enable this synchronization to be done automatically by the devices with greater accuracy.
  • New compressed audio formats: In addition to HDMI's current ability to support high-bandwidth uncompressed digital audio and all currently-available compressed formats (such as Dolby Digital and DTS), HDMI will add additional support for new compressed digital audio formats Dolby TrueHD and DTS-HD.

Now, all of these things sound very cool, especially the new mini-HDMI connector, but the two things of greatest interest for high-definition TV are the first and last items. To wit, (1) higher speed, and (2) support for new audio formats.

I'm using the press release for my analysis, as well as other open-source references, because you've got to be a manufacturer to get a copy of the published HDMI 1.2 specification (forget the not-yet-released 1.3 version). So it's a read-between-the-lines thing.

So, higher speed. "Though HDMI has more than twice the bandwidth needed to support all HDTV formats, HDMI will increase its single-link bandwidth to support the demands of future HD display devices, such as higher resolutions, deep color and high frame rates."

Frame rates?

When it says "bandwidth needed to support all HDTV formats," one would assume they meant to include 1080p, right? Well, actually, if you're talking about the ATSC digital TV standard, the included HDTV video specifications for 1920 x 1080 displays include 60i, 30p, and 24p. The numbers are frame rates, the "i" and "p" of course designate either interlaced or progressive.

The specs for 1280 x 720, on the other hand, are 60p, 30p, and 24p.

Broadcast digital HD is either 1080i or 720p.* CBS and NBC use 1080i, with a frame rate of 30 frames per second, and ABC and Fox use 720p, at 60 fps. Full-specification HD (1920 x 1080) has more than double the pixels of 720p HD, so you get a lot more detail in the picture, but 720p puts twice as many frames up on the screen every second. 720p is therefore better for video containing fast action, such as sports. The action is smoother.

The data rate between the two formats is similar. 1080i has more than twice the pixels per frame, but 720p has twice as many frames. HDMI specs talk about data rates. One format is not really harder than the other.

1080p is another animal, and it's not part of the ATSC digital TV standard. One must presume that it is 60p--60 frames per second with progressive scanning. The ATSC talks about 1080/60i, which is 60 fields per second. Each field is odd or even lines; two fields make up a full frame. Therefore 60i is 30 frames per second. 1080p is 60 fps, or double the data rate of either 1080i or 720p.

The press release for HDMI 1.3 says "higher speed" to support higher resolutions and high frame rates. So where do we find those requirements? 1080p. In other words, high-definition DVDs (Blu-ray Disc, and HD-DVD).

The new high-definition players

The Toshiba HD-DVD players will be available April 18 (would have been on sale March 28 if HD-DVD movies had been ready.) Those players will not output 1080p, only 1080i.

Blu-ray players are expected to ease their way to market. The first Samsung player will hit stores on the day Blu-ray rolls out--May 23. Specs on that player seem to be up in the air, with at least some reports saying it will output only 1080i. Oops! Samung has now decided to release the player on June 25. They say to better test the player with Blu-ray movies, but maybe also a possible wait for HDMI 1.3 and upgrade to 1080p? And now (as of 4/7) it turns out that Samsung is going to upgrade their player to 1080p!

So now with no players to be out on May 23, will Blu-ray also postpone the release of the Blu-ray movies? I wouldn't be surprised.

Other Blu-ray players are said to include 1080p output: Pioneer in June but now may be delayed; Sony in July; Panasonic in September.

There seems to be a trend here. Players before June can't output 1080i; those coming later can. Could it be that the timing for the 1080p players is dependent on the HDMI 1.3 spec being finished? (reported in early January as being ready during the first half of 2006)

1080p TVs

The part of this puzzle that doesn't fit is that 1080p television sets are now available. True, many of these reportedly will not accept a 1080p signal, but will convert the input 1080i signal to 1080p for display. (But that's a given for fixed-pixel displays.)

The Samsung HL-S5679W is a 56-inch DLP set that uses an LED light source, reportedly available in April. Its dual HDMI inputs claim to support 1080p sources.

Other sets make the same claims (some very expensive).

On March 6, Vativ Technologies, Inc. announced an HDMI receiver chip permitting the connection of three independent HDMI input sources. The chip will decode two of those sources simultaneously, enabling high-def picture-in-picture (PIP).

What is important for this report is that the chip is fully compliant to the HDMI 1.2 standard and that it supports 1080p. Volume production is said to start during the second quarter this year, i.e. any time up through June. Have they designed in the expected specifications for HDMI 1.3?

Or it could be that the "send" portion (for sources) of the HDMI standard is lagging behind the "receive" part (for displays)(although that seems odd).

The New Audio Formats

Okay, so going back to the HDMI 1.3 press release, and that last upgraded feature.

"In addition to HDMI's current ability to support high-bandwidth uncompressed digital audio and all currently-available compressed formats (such as Dolby Digital and DTS), HDMI will add additional support for new compressed digital audio formats Dolby TrueHD and DTS-HD."

These are the new audio formats that have been embraced by HD-DVD and Blu-ray Disc:

  • "Dolby TrueHD is Dolby's next-generation lossless technology developed for high-definition disc-based media. Dolby TrueHD delivers tantalizing sound that is bit-for-bit identical to the studio master, unlocking the true high-definition entertainment experience on next-generation discs. . . Supports up to eight full-range channels of 24-bit/96 kHz audio . . . Up to 18 Mbps bit rate." (from Dolby's web site)
  • "Dolby Digital Plus is the next-generation audio technology for all high-definition programming and media. It combines the efficiency to meet future broadcast demands with the power and flexibility to realize the full audio potential of the upcoming high-definition experience. . . Channel and program extensions can carry multichannel audio programs of up to 7.1 channels . . . Supports data rates as high as 6 Mbps." (from Dolby's web site)
  • DTS-HD (sometimes with "Master Audio" suffix) offers 7.1 discrete channels of 24-bit/192 kHz sound. ". . . indistinguishable from the original master" (from DTS promo material)

If you don't have HDMI 1.3, you won't hear it. Of course, if you've got a home-theater-in-a-box audio system, you won't get the full benefit even if you do have HDMI 1.3.

If you DON'T have HDMI 1.3, will there be an upgrade available (through firmware downloads or whatever)? Don't know. Not clear. Check with the manufacturer.

Of course, right now NOBODY has HDMI 1.3; my statement was forward-looking.

Consumer electronics manufacturers and retail outlets don't want you to know what's just around the corner because they don't want you to stop buying new stuff today.

Good luck, and stay tuned!

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* 1080p is not included in the ATSC digital broadcast standard, yet. Broadcast TV is constrained by 6 MHz TV channels (limited bandwidth) and the MPEG-2 video compression protocol that is written into the ATSC standard.

With MPEG-2 efficiencies and the 6 MHz bandwidth limitation, there is no way to get the required data rate for 1080p/60 broadcasts. The satellite people, faced with the need to add tons of new high-def channels to their limited satellite capacity, switched from MPEG-2 to the much more efficient MPEG-4 compression protocol.

All they had to do was change their compression equipment and arrange for all of their high-definition customers to get new HD/MPEG-4 receivers.

The broadcast and TV manufacturing industries are not likely to make that sort of switch anytime soon. Sure, TVs could start coming with both MPEG-2 and MPEG-4 decoders built-in, but broadcasters don't seem to be very interested in improving video quality.

In fact, when faced with the choice of airing a single high-def channel or five standard definition channels, the broadcasters as often as not have opted for the five channels (5 chances to sell advertising). They do usually go with the high-def for prime time shows, but some networks have been scrimping on their high-def broadcast data rate in order to air a second standard-def program at the same time.

So if the ATSC standard was amended to permit MPEG-4, and it was implemented, the broadcasters would almost certainly use the added efficiency to add several more simultaneous standard-def channels to the one high-def channel, instead of upgrading their HD to 1080p.