HDMI - DVI conversion

[blueboxoffroad]

Hi there - I have been asked by a client to look at the options for distributing an HDTV signal to a network of 50 (yes 50) plasma screens in a conference venue. I have 2 main problems: I don't know what the spec of the forthcoming Sky HDTv signal (which is what we'll be running to the system) and the screens don't have a HDMI input, but do have a DVI input I could access. Short of replacing the video card in each screen (and I don't think LG had that in mind when they designed the screens!) does anyone have any experience with this kind if challenge? Thanks

[Pete McCrea]

Are these screens currently installed and wired, or will they all be installed for the event? How close will they be? If they are rigged in groups, then it will be easier to distribute as you can use a spine type distribution.

 

DVI Signals are hard to distribute. According to the guys at Kramer, after about 5m over copper wire DVI cables, the signal just stops getting transmitted (I guess it drops off to the point where the signal can't be interpreted by the reciever). They and several others have started selling a DVI to DVI fibre cable which converts from electrical to fibre in the (fairly big) DVI connectors. They ain't a cheap option, and maybe better for installation where they are less likely to get damaged.

 

The other option might be a wireless system. I saw a system at ISE that used the 5GHz spectrum, and offered OK signal transmission. But your looking a several hundred per RX. One TX will server about 8RX from memory.

 

I don't know if there is a cheap option to keep the quality and distribute to all the screens. I'd have thought that you'll have to compromise somewhere to achieve this. You might be lucky and have a client that will acept that Quality=Cost. Good luck if you have!

[Tomo]

From what I've gathered over the last few months, HDMI is basically DVI bundled with audio in the same cable, but with copy protection as well.

 

This is likely to mean that certain channels (probably pay-per-view and the like) can't be distributed at all, just to make life even more difficult.

Thankfully the UK doesn't have a DMCA, so it's possible that suitable kit to circumvent this protection will be available.

[back_ache]

the options for distributing an HDTV signal to a network of 50 (yes 50) plasma screens

 

Hello to a fellow South East Londoner!

 

Okay a few questions and then some answer, first the questions :-

 

* Are all the screens to show the same thing all the time?

 

* How many and what kind of input sources will they be?

 

* Are they happy to turn the control and monitor the screens manually, or do they want in done automatically?

 

* what are the models of the screens?

 

* is this to be operated by technicians or civilians?

 

* how far away is the furthest screen and what length cable would be required to get there?

 

* what cabling is in place at the moment

 

* is this a temporary or permanent install

 

Okay, now some answers about Sky HD

 

* Sky HD outputs on a connector called HDMI, it looks like a USB connector but carrys a DVI-D and a digital audio feed.

 

* The DVI-D standard allows a copy protection scheme called HDCP to be emmeded in the signal.

 

So in theory at least (and depending on your model of screen) your should be able to convert Sky's signal to DVI-D to go into your screens, though how to transport the signal that distance and many times will need those questions answering.

 

My first thought is to run your sources into a scaler, then a distribution amp, then over cat 5 using something like this that will take the signal 150ft (they claim) http://www.gefen.com/kvm/product.jsp?prod_id=2515 to control the whole lot use an AMX solution or a PC running stardraw control

[BlueShift]

HDMI to DVI converters arent too hard to come by, so that is always an option, then you need to be looking at using some kind of cat5 or fibre based signal distribution system.

 

Now assuming you want to have 50 mirrored screens (50 plasmas all displaying the same thing) you have a few options.

 

Firstly, if you only want to cater for the 720i/p coming out of sky HD (correct me if im wrong but atm skyHD does not support 1080 in any form), which I assume you are since its highly unlikely you have 50 plasmas capable of 1080 vertical lines, then it may be worth looking at running it over an analog signal (a-la WXGA on HD15 connectors) as this is far far easier to distribute and still gives the full resolution of the HD signals. You can then run a tiered distribution system with Cat5e/Cat6 being run out along the major runs and then have local distribution via RGBHV D/A 's

 

If going digital is a must (you would struggle to get great quality 1080 pictures down an analog link for sensible money) then I would say that fibre is the way to go, or alternativly, you could scale everything to HD-SDI and then you can get a great picture and audio down a single piece of coax.

 

Basically, more info is required about the grouping and relative locations of the scteens as well as what the goals of this system are, as back-ache says, are we taliking 50 mirrored screens or is the sky HD merely populating one of several inputs?

 

Cheers

[back_ache]

I've just checked sky hd faq they will be pumping out both 720p and 1080i and "most" of the content will have HDCP embedded.

 

I was suggesting pumping it through a scaler to abstract the sources resolution from the displays resolution, to act as a switch and to support "legacy" sources.

 

So a simple way would be to convert to analog VGA(sic) and distribute using the 101 solutions out there for getting analog VGA to remote locations.

 

My worry is analog is going to be more susceptable to inducted noise but it should be easier to drive long distances and to get hold of a matrix switch if the screens are to show different content.

 

I would suggest also sending a serial control signal to each screen, fifty is a lot to look after manually unless like me you need the exercise :)

[blueboxoffroad]

Wow - thanks guys for your input! The screens are installed LG's (sorry no model number as yet) and as part of the overall TV offering they have three Sky boxes on fixed channels (I have the power to retune!) Currently it is all set up with an RF network, but I have yet to see how this is configured. Maximum runs are probably in the order of 100m (by the time its run through the risers etc) All the screens are currently controllable from a central piece of software and a Cat 5e Smart-e network, so, even though I too could do with the excercise, I can control the entire system from a single point.

[back_ache]

Wow - thanks guys for your input! The screens are installed LG's (sorry no model number as yet) and as part of the overall TV offering they have three Sky boxes on fixed channels (I have the power to retune!) Currently it is all set up with an RF network, but I have yet to see how this is configured. Maximum runs are probably in the order of 100m (by the time its run through the risers etc) All the screens are currently controllable from a central piece of software and a Cat 5e Smart-e network, so, even though I too could do with the excercise, I can control the entire system from a single point.

 

If they are using a smart-e maybe the simplest way would be to use a HDCP compatable hdmi-vga convertor into the matrix switch.

[Ellis]

All HD signals on Sky are also being simulcast in SD. The fact that you are specifying HD tells me that you are doing an event that is marketing HD in particular - i.e. high quality and keeping the HD format is essential.

 

If you are working on an event marketing HD, can you get modified sky HD boxes without HDCP on the output on loan from Sky? Or can you get tem to narrowcast a non-HDCP transport stream for you (restricted to your viewing cards). They have a vested interest in HD being shown at its best! I have heard that HD signals will only be available on the HDMI port, so no other output will work.

 

The whole point of HDCP is to prevent HD piracy by intercepting the HDMI signals and re-encoding into MPEG. It is highly unlikely that a stand-alone decode will ever be commercially available - pirates have lots of money to buy such kit!. Attempting to circumvent copy protection is illegal throughout Europe - we have out own equivalent of the DMCA!

 

You may be lucky with the HDCP - if you are having a special signal narrowcast for you, the narrowcaster should be able to specify HDCP OFF - then you've just got the hastle of distributing the unencrypted signal.

 

If you do have an HDTV narrowcast, can you have it transmitted in the clear - if so, you could use three PCs with HD satellite cards and standard WXGA distribution techniques.

[back_ache]

It is highly unlikely that a stand-alone decode will ever be commercially available - pirates have lots of money to buy such kit!.

 

Okay hands-up!

 

The box I found that was touted as HDCP compatable I have just found was being misrepresented by the supplier

 

The supplier said

 

"DC-DA1 is HDCP compliant and can be used with devices that use this copy protection feature"

 

The manufacturer said

 

"This device is not HDCP compliant."

 

Grr...

 

sigma had a good page for describing HDMI

 

 

I have no doubt HDCP stripping HDMI-VGA convertors will be around however their legality is dubious so I guess you are back to DVI-D/HDMI distribution

[Ellis]

For those that can understand such things, the HDCP specification is available online Here.

 

A brief summary:

 

Each device has a unique identity.

The data stream between devices is encrypted with keys that are unique to the device pairing.

To drive multiple displays from one source, you will require an 'HDCP repeater' - essentially pairs with the source, decodes the signal and then re-encodes on several different outputs for the paired displays.

HDCP wil only ever be licenced to be included in a source or display device (or a repeater) - licencing includes the issuing of ID codes and individual device keys

The specification includes a means to deactivate compromised equipment - a hacked display device will be black-listed on all HD-DVDs and HD Broadcasts.

 

With that sort of robustness designed in, no-one will want to break it by licencing devices that compromise it.

[back_ache]

With that sort of robustness designed in, no-one will want to break it by licencing devices that compromise it.

 

When it gets in the way of people getting in the way of doing perfectly legitmate things it is setting itself up for mass civil disobediance as happened with home taping and DVD regionalisation.

 

Maybe as pro's we should just ignore HDMI and use other interfaces till it sorts itself out.

[back_ache]

Rumor has it, the first generation and the first generation only of the Sky HD box will have a componant output and that output will output at HD resolution, take that, covert to VGA then into your matrix switch and bobs your uncle.