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Trying to understand HDMI

upstatemike

Senior Member
Anybody using HDMI very much? I'm trying to study up on it but so far I'm having a hard time sorting out the details. This is my understanding so far:

*It has a 15 meter cable length limit so it is not suitable for distributed A/V.

*It combines audio and video in one cable making it difficult to use discrete components such as an outboard sound processor or stand-alone video switch.

*Most of the technology behind the spec is dedicated to DRM rather than A/V transmission quality.

*The current 19 pin HDMI A standard is about to be superceded by a 29 pin HDMI B standard so any investment in HDMI equipment is almost instantly obsolete.

So I guess what I'm asking is: Is it enough of a quality improvement over Component Video to overcome the points above? And how are people pre-wiring for HDMI?
 

dublin00

Member
HDMI is a child of Intel's original DVI spec which was designed as a simple digital interconnect between a PC graphics card and a LCD flat panel monitor.

The original Intel DVI spec even included the old VGA red/green/blue analog signals for backward compatibility with the 15-pin VGA connection we all know from the PC world. This immediately led to the confusion of DVI-I and DVI-D which stood for equipment/cables that only supported the analog signals or the digital signals respectively. Hint: originally Intel wanted everyone to always support both analog and digital signals on DVI, but some manufactures didn't want to do that for whatever reasons, but I digress...

Your correct that HDMI was created mostly as a way to provide DRM protection, and a very important reason was to include encrypted audio which DVI couldn't support since it was only designed as a connection between a PC graphics card and a monitor. This was something that the MPAA wanted to protect future digital audio content. The HDMI specification also drops all support for VGA analog video and adds mandatory HDCP/DRM protection (at least your supposed to provide it).

The problem with trying to run HDMI cables very far is that it is a pretty simple low voltage differential signaling system (lookup TMDS on the Internet). The electrical interface does not include any support for driving long distances since it was originally designed to just connect a monitor (aka TV) to a PC (aka set-top box, DVD player, etc..) and to be as "cheap" as possible. The manufactures also wanted to cabling to be as cheap as dirt which is why they used in-expensive twisted pair cabling (yes, those expensive HDMI cables at BestBuy are really just fancy twisted pair cables like CAT5 but with more pairs and a slightly different electrical specification).

I haven't heard anything about a new HDMI connector, but that could be for future higher resolution displays. SONY for instance is already talking about an ultra high definition TV system with 7Kx4K resolution or something crazy like that. One of my trade rags mentioned that, but it is just a technology demo at this point. I can't imagine the current connector going away anytime soon since most of the equipment makers are only now really gearing up to push HDMI mainstream.

Even without a new connector HDMI already has three specification revs and it is almost impossible to find out which spec a manufactured used. For instance, people in the cable TV forums on the Internet are already complaining that new set-top boxes with HDMI outputs won't talk to the latest HDMI switching A/V receivers. All caused by the set-top boxes using an older rev of the specification that didn't yet have the support for HDMI switching. You get the picture.
 

AccessX10

Member
Mike,

Sounds like you have a pretty good handle on HDMI. I just received a 35ft HDMI cable the other day. Testing against VGA, DVI and Component from a video perspective… I have a hard time telling the difference.

However, HDMI is the only digital interface for consumer electronics that can carry uncompressed HD video, multi channel audio, intelligent format & command data. So a single cable that can transmit a lot of information.
 

upstatemike

Senior Member
dublin00-

Great overview, thanks!

Now the $64K question: If I am happy with component video will I be able to stick with that or will all future hardware support HDMI only?

AccessX10-

It's a lot of information but only over a very short distance. I'm still not clear how you pre-wire for whole house HDTV in the HDMI world of the (near) future.
 

dublin00

Member
upstatemike said:
Now the $64K question: If I am happy with component video will I be able to stick with that or will all future hardware support HDMI only!
I think that for the next few years analog component video is here to stay.

The only real problem is going to be HD-DVD/Blu-Ray. Originally the MPAA only wanted the players to output 480p on the component video jacks, but that was suicide for a new media format, so they backed off.

BUT, the current specs for those new HD DVD formats include a set of encrypted keys that control various features on the player. I personally find this offensive, but one of those keys allows the content provider to disable HD video on the component video jacks. What this means is that they could at anytime start pressing HD DVD discs with that encrypted key included and you would then only be able to watch the video in high definition on the encrypted HDMI interface (i.e. the analog component video jacks would only output a 480p resolution picture).
 

dublin00

Member
upstatemike said:
So I guess what I'm asking is: Is it enough of a quality improvement over Component Video to overcome the points above?
BTW, the only real difference in video quality between component video and HDMI in theory is HDMI's ability to indicate a "true" black. If you've ever calibrated your display using one of those DVDs they sometime call this blacker-than-black. The HDMI digital stream can pass a code to the display telling it that a pixel is true black which isn't possible on analog component video.

Honestly, depending on your display it maybe impossible to tell the difference. I'd love to hear how much success people have bad calibrating the black level on their HDTV displays though.
 

AccessX10

Member
upstatemike said:
It's a lot of information but only over a very short distance. I'm still not clear how you pre-wire for whole house HDTV in the HDMI world of the (near) future.
I agree... 50ft is the max for a high quality HDMI cable. To go beyond you will need a repeater like this:

http://www.uniqueproductsonline.com/hdmirepeater.html

But that will only buy you about another 50ft - 75ft. It's definitely not ready for whole house distribution.
 

dublin00

Member
upstatemike said:
dublin00 said:
Here is an article on the Toshiba player that makes the component issue pretty clear:

http://blog.scifi.com/tech/archives/toshib...nrez_issue.html
I assume that the same people who produce region-free DVD players will be soon be selling down-rez disabled ones?
I'm sure they will try, but the MPAA has the Digital Copyright Millenium Act to help them knock-off anyone that tries to get around the DRM. I'm afraid it is going to be a lot harder for those same people to import those down-rez free products this time. :D
 

electron

Administrator
Staff member
and they can block any 'hacks' in future DVD releases from what I can tell ... this really sucks for the consumer.
 

jlehnert

Active Member
Hey E,

HDMI is one thing I completely left out of the wiring guide, mainly because I don't know anything about it other than how to spell it (Let me see now, that's "HDMY"?).
 

upstatemike

Senior Member
electron said:
I am really getting tired of the consumer being punished in advance in an attempt to stop piracy (which won't happen anyways).
So to summarize: DRM is pre-emptive action against innocent people in an attempt to address a perceived grievance against some other group that cannot be confronted directly?

Isn't that the definition of terrorism? So what does that make HDMI, a Weapon of Mass Destruction?
 

electron

Administrator
Staff member
Terrorism, racketeering, you name it, it's bad, and it's depressing because most consumers will just accept it.
 
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