Forum Archive Home -> Digital TV / DVB / HDTV -> Connect LCD monitor to Digital HD Cable box?
| Connect LCD monitor to Digital HD Cable box? | ||||
| rogerconnery posted 2006 Nov 12 20:55 | ||||
| Hi all,
I have a newbie question (did a search and couldn't find anything relevant): I have a widescreen 19" LCD monitor with 1440x900 resolution. There is no TV tuner of any kind. It has DVI and VGA out. I have a Digital HD Cable box with HDMI in. I was wondering if it is possible to connect the monitor --> DVI out --> HDMI adapter --> Cable Box (HDMI in). I have tried this method, but my screen is blank. No signal comes on. Is it generally possible to watch cable/HD cable through a computer monitor, or am I missing a step in my connection here? Thanks in advance! | ||||
| edDV posted 2006 Nov 12 21:38 | ||||
1. An LCD monitor does not have DVI out, only in. 2. A cable box has HDMI out but not in. The two do not connect directly. HDMI out from a cable box is 480i, 480p, 720p, 1080i @59.94 hz. normally. A computer monitor only understands VESA progressive resolutions and frame rates. "Generally possible" no. But it makes a great science fair project. The normal way to do it is to put a computer in the middle with a display card feeding the computer monitor via DVI-D. Getting the cable box HDMI into the computer is the rub. | ||||
| rogerconnery posted 2006 Nov 13 08:56 | ||||
| Thanks for the help!
Just a technical question: why is a computer necessary to act as an intermediary between HD cable box and monitor? If the Box has an HDMI out, and would connect to the PC, wouldn't it also work for the monitor (albeit DVI in)? The only problem I could foresee would be to "translate" the HDMI into DVI, which an adapter would be all that it takes, no? Correct me if I'm wrong. Thanks again! | ||||
| edDV posted 2006 Nov 13 13:38 | ||||
First, if it was their intention, the cable/dbs box manufacturers could easily support normal DVI computer monitor (VESA) resolutions over a DVI or HDMI port. But that is not their intention due to protests by media rights holders, program distributors and the government. The last step to totally sealing up this port is HDCP encryption which hasn't yet passed US Congress and the legislatures in other countries but the technology is built in to all HDMI connections. Cable and DBS companies can implement the technology on their own programming. It is a gray area whether they can apply HDCP to local rebroadcasts without the brodacast flag legislation. You cannot connect the HDMI out to a computer input. There are no DVI or HDMI inputs on a computer. If you make a device that that bridges the gap, you are potentially violating US federal law. Cable and DBS boxes usually output: 720x480i (interlace) 720x480p (progressive) 1280x720p (progressive) 1920x1080i (interlace) Digital TV sets include deinterlacers and scalers to convert these inputs to the native display technology. Computer monitors accept only DVI-D VESA resolutions and provide scaling technology only. A computer monitor will not accept an interlace input. It would be possible to build a computer monitor that directly accepts 720x480p, or 1280x720p but most don't. Computer monitors assume that TV like controls are in an upstream computer display card. They provide no aspect ratio, overscan or TV gamma processing that would be standard in any HDTV. http://en.wikipedia.org/wiki/DVI http://en.wikipedia.org/wiki/HDMI http://en.wikipedia.org/wiki/HDCP http://www.eff.org/IP/broadcastflag/ | ||||
| rogerconnery posted 2006 Nov 13 15:44 | ||||
| Wow, thanks so much for the insight.
The only reason I was so confused here is because I have a 42" Sony Plasma (capable of 720p and 1080i) with an HDMI in. We connect that to our HD Cable box's DVI-out (via HDMI->DVI adapter). That works with no problems at all. However, when I try the monitor set up (mentioned above) I get a blank screen. I thought all DVI was created equal. I guess not, huh? Thanks again! | ||||
| edDV posted 2006 Nov 13 15:49 | ||||
You mean for the computer monitor? Any DVI-D/HDMI input has something called the port ROM. This defines exactly what the port will accept and rejects everything else. | ||||
| rogerconnery posted 2006 Nov 13 17:50 | ||||
| (HD Cable box --> HDMI out --> DVI adapter --> DVI wire -- DVI in to Monitor)
So if my monitor's DVI "port rom" rejects an HD Cable box's signal, then I would get no images and hence the blank screen? | ||||
| edDV posted 2006 Nov 13 17:57 | ||||
Yes. It might work for 480p. They won't get sued for that. 720p might work*. Computers do this in software drivers. Those can be updated. Hardware devices do it from ROM (read only memory). Replacing ROM often gets into soldering. * The power politics of this requires all manufacturers to do it together but it can't look like they ever talked or they could be put in jail for anti-trust. It's sorta like airline ticket prices. If they (chinese-taiwan-walmart-bestbuy-vizio-costco, ...) all do it one night, the MPAA would seek out the weakest little guy and sue him in order to set a precident. The others would offer legal support or retreat. We need legal guys to wade in now. | ||||
| apex89 posted 2007 Sep 19 03:00 | ||||
| Will the gadget from Startech VID2DVIDTV Composite/S-Video/Component(YCbCr) to DVI-D/HDTV Converter can be used between LCD monitor with DVI-D input and HD cable box? | ||||
| apex89 posted 2007 Sep 19 03:10 | ||||
| sorry guys.....having read the queries about using a LCD computer monitor for the HD cable box, will the gadget from Startech VID2DVIDTV Composite/S-Video/Component(YCbCr) to DVI-D/HDTV Converter can be utilized/ used to have the LCD Computer Monitor work as an HD monitor? Will a computer monitor understands the cable box HD output as a VESA progressive resolutions/ frame rates usiing this gadget? Thanks.... | ||||
| edDV posted 2007 Sep 19 12:20 | ||||
| I don't know about that $430 box. The Startech VID2DVIDTV looks to be a 1280x1024 box with scaling for 1280x720p and a scaled "pseudo-interlaced" 1080i.
For less money you can get an LCD computer monitor with HDCP such as the new Samasung 226BW http://www.samsung.com/us/consumer/detail/spec.do?group=computers ... fullspec=F It will directly accept my cable box 1280x720p or 720x480p DVI outputs and internally scale to native 1650x1050 in 16x10 (mild vertical stretch and overscan). It seems to work fine with 16X9 and 4x3 material (side pillars) fron the cable box. Picture quality is good but it lacks the video processing features of the current Samsung LCD-TV line that gets the enhanced blacks and separate adjustments per input. As it stands its difficult to get a monitor adjustment that works perfectly for both cable DVI and computer but is accceptable as a TV display. | ||||
| bigbadleroy posted 2007 Dec 03 16:09 | ||||
| After you connect the dvi from your cable box to the lcd monitor what do you connect for the audio? Regular composite cables? | ||||
| edDV posted 2007 Dec 03 17:27 | ||||
This is a very old thread in tech dog years. Since then some LCD computer monitors (e.g. the Samsung 226bw that I own) support HDCP and scale 720p and 480p DVI video from cable/sat boxes to full screen 16:9 or more likely 16:10 for display. You can still hear all those Apple Cinema Display owners crying that you need a computer to make those useful. Apple never mentions or warns about HDCP. There are still disadvantages to forcing a computer monitor to pretend to be a TV. First the 16:10 issue for 1680x1050 native display. People stand a bit tall and thin at 16:10. If you adjust the monitor for letterbox 16:9, then your computer runs as letterbox. Second, a computer LCD can't force the dynamic contrast backlight tricks found in LCD-TV sets so black levels and contrast are marginal when connected directly to an HD cable box. Some computer LCD monitors have audio input and tiny stereo speakers but they are weak for TV. You need a separate amplified speaker setup. Simple stereo is easy. 5.1 needs a S/PDIF (coax or optical) connection. | ||||
| Darryl_Licht posted 2008 Jan 07 18:11 | ||||
:?: :?: :?: Did you have to make any changes to your resolution on your set top box? If, so what worked? I tried this earlier today and got an error that my resolution was incorrect. My native resolution is also 1650 x 1050 on my HDCP Sammy 206BW.  [/quote] | ||||
| keyosuke posted 2008 Sep 11 09:30 | ||||
Yeah, this thread really is somewhat out of date. I read threads like this and assumed I couldn't plug my cablebox HDMI out into my monitors DVI in, which lead me to a week of playing with sending the signal over firewire and I bought a cheap 7 dollar firewire cards to do it. In the end I was disappointed with the firewire method because my cable provider, Verizon, was blocking over 90% of the channels they offer when viewed over the firewire port. The final solution was an adapter I found under my bed that takes HDMI in and provides DVI out. It works well since my monitor can pretend to be a TV quite well, even though it's the cheapest model of ACER monitor I could get my hands on. If a cheap ACER LCD flat panel can take HDMI via a small cheap adapter into a DVI port, then I'm guessing any monitor these days has a good chance of doing that. Incidentally, I can watch every single channel like this and my black seems black and colors seem vibrant. The angle of view from top to bottom is terrible but that's because the monitor is a cheap sale item. The cable box also supports multiple output formats like 480i 720i etc and the monitor recognizes two of the four and works fine with them. If I make a mistake and set it to a mode the monitor can't handle, I just unplug both devices and life is good once more. | ||||
| edDV posted 2008 Sep 11 13:42 | ||||
The main point from above is most cable boxes require an HDCP connection or they won't send 480p, 720p or 1080i. A normal computer monitor won't accept 480i. My Motorola HD cable box goes to blue screen and flashes "HDCP" on the LED display when connected to a non-HDCP computer display (e.g. Viewsonic VA912b LCD). Either your ACER LCD monitor has HDCP support or your cable box doesn't require HDCP. http://en.wikipedia.org/wiki/HDCP | ||||
| keyosuke posted 2008 Sep 11 13:52 | ||||
| The answer to your OR is that my monitor supports HDCP, and the point I was making is that it is some cheap ACER garbage edition I got on super low discount that exudes an ora of "I will break immediately after the 1 month warrantee", and yet it still supports HDCP. Hence, the real point is that monitors these days tend to support it, or my motorola box which is probably the exact same one you have (I'd love to compare hardware if it makes you feel better) doesn't send data over the HDMI cable with HDCP. I've read the documentation on my particular model and the model it's derived from and it's definately capable of HDCP, and that means my cheap monitor is handling the HDCP just fine, thank you. And that means my point that people should at least give it a try on their monitors since it's not a rare and costly feature these days, is a valid point. I hope I've cleared up what I was trying to say with my first post and I hope you see the point now.
Why did I make this point? Because I was lead to believe that the odds of my monitor supporting HDCP were very bad odds. The masses of posts on the internet about this topic lead me to waste my time believing that and I wanted to make sure anyone reading this post sees that it isn't necessarily rare to have HDCP support and that people in general might want to try an HDMI to DVI adapter since it just might be a great solution. Thanks | ||||
| edDV posted 2008 Sep 12 02:39 | ||||
| HDCP support on computer monitors is a recent trend. Samsung seems to be on the leading edge but others, even budget models include HDCP chipset support* while even the most expensive older models lack HDCP (e.g. Apple, Dell reference monitors).
You need to review the specs if you are buying a new or used computer monitor. This can be problematic because HDCP support is often missing in the printed technical specs. I'm looking at current Apple Cinema Displays ($599-$1799) as an example. These monitors are nice for HD video production but will they connect to a cable box or BluRay player? The specs don't tell. I make it a point to ask Apple store sales people (who then consult the "genius") whether Apple displays support HDCP? The answer has always been they don't know. I'll grant I haven't been in an Apple store since I bought my mom a mini Mac last Dec. http://www.apple.com/displays/specs.html 
No mention of HDCP support. So let us try Dell. Ahh good. The Dell Crystal series does have HDCP! 
Note that any device that has an HDMI port must have HDCP enabled. It is part of the HDMI spec. DVI-D ports may or may not have HDCP. * Chipset support isn't enough for HDCP. The monitor manufacturer needs to licence and register the implemtation with Intel's Digital Content Protection, LLC subsidiary and pay a fee. HDCP is an active encryption scheme that requires a verified key unique to the device. HD resolutions are inhibited at the source until HDCP authentication is verified. There is even a process for key revocation if it is suspected a device has been compromised. Key revocation lists can be distributed in software updates and even on retail DVD/BluRay discs. |
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