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HDTV-DVI Protocol Interpretation?
ignipotentis asks: "I have recently been looking into getting a Sony 50" Grand Wega. However, the one thing that deters me is the lack of obvious PC support. I would like to use the TV as a monitor for a living room PC as well as a TV. So I set off to do some investigation. I came across the ATI Component Adapters and then came across the reviews stating their overscan problems. Next I decided to check out the details on DVI (DVI & HDCP) and I've become rather confused. From what I gather, HDTV-DVI is nothing but DVI-D + HDCP. Now, being DVI-D, it can accept a signal from any DVI-I video card as long as a DVI-D male to male cable is used. Where I become confused is in the HDCP protocol. The way I read it, the Host (my computer) in this case, initiates the authenticity check whenever it wants. If it doesn't receive a valid reply, it can stop the stream. However, nothing is stated (that I can see) as to what would happen if no check was ever performed. If the Client (the TV) just continues to display what it receives, then all is good. If it does not, then I guess I'm back to the drawing board looking for other TVs. My question to Slashdot regards that of the protocol. I've emailed info@digital-cp.com only to getan automated response as a reply and I'm hoping that someone a bit more technically savvy than myself can interpret the HDCP protocol better than I have been able to."
From what I understand, you're right -- an HDCP-compliant TV will not reject a non-HDCP signal. At least that's what I've been told. I recently purchased a Sony HDTV (46" rear proj.) with DVI-HDCP, and I've been told (on a mailing list) that it *is* compatible with computer outputs, provided you get your computer to send the right kind of signal. Because this is tricky, the "official" word from Sony is that the set doesn't support computers.
I haven't tried looking for the right kind of cable -- I know there are different kinds of DVI connectors, and the TV's connector is likely different from what's on my video card. One of these days, I'll probably give it a shot.
BTW, I was surprised when I dug into the DVI spec -- it's nothing more than a digitized raster signal. I'd expected something a bit more structured, somehow, like (x,y,r,g,b) data. (though I didn't see anything about how HDCP worked).
It seems the real advantage of DVI over, say, an RGB/VGA connection, is that the pixel levels are exact-digital (as opposed to a varying voltage level) and the digital format (with error correction) is less prone to noise. Or am I missing something? Because unless it allows for direct mapping of pixels, I don't see why DVI would be more precise for, say, an LCD panel, than a very clean VGA signal.
david.
My friend got a 50 inch sony LCD Projection widescreen TV. He and I messed around with timings using power strip for hours and hours using the DVI interface. When we would push it too far the image would disappear. Quite frustrating when you have to reboot the box each time. But when we used the component video out of the video card (ATI AIW 9700) , It worked like a champ! Even if we "over drove" the display... the resoultion went virtual.
I doubt any current PC Video cards implement HDCP, however, I doubt any current TVs will REQUIRE it in order to accept a signal. You are much more likely to have problems outputting a resolution that the TV will display than an issue with HDCP.
There are better forums to ask this question, such as The AVS Forum and The Home Theater Forum
Just buy a 64Mb version of the 8500 (fairly cheap and falling fast) and one of these things here. And off you go to HDTV PC viewing.
That's not a bad investment next to a $4000 TV.
Operator, give me the number for 911!
Check this out. It's the home page for Digital Content Protection, LLC -- the folks who administer the HDCP protocol licensing system. At this site you'll find HDCP's specifications, upstream protocol, license agreements, reseller agreements, etc.
Of interest, also, may be Niels Ferguson's paper in which he details the cryptographic weaknesses in HDCP. Unfortunately, he won't publish the document due to fears of being prosecuted under the US DMCA.