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Displayport: A Better Video Interface

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Re: Displayport: A Better Video Interface

#241

Post by Fnoord »

xxpor wrote: post #108
tivert wrote: post #77

Are there any KVM switches that do Displayport well (i.e. where switching between inputs does not look like a display disconnect to the PC)? I'm still using HDMI because I like to share my home multi-monitor setup between my personal machine and my work laptop, and the KVM switches are able to fool the PCs into thinking the monitor are always connected. Years ago I tried a Displayport switch, but it could not -- I as…

The magic words you're looking for are "EDID emulation". The KVM will continue to send the EDID data from the monitor even after you've switched away, which will fix that issue. It's relatively uncommon and not always implemented super well, but it's a requirement for any DP KVM to be not super annoying IMO. There was one particular KVM brand that was supposed to do it well whose name is escaping me now :/. I was loo…

BliKVM PCIe I bought (based on PiKVM) came with an EDID emulator.

Re: Displayport: A Better Video Interface

#242

Post by angry_octet »

madars wrote: post #200
TazeTSchnitzel wrote: post #143

The amazing thing about DVI, and by extension HDMI, is that it's just VGA but digital, with all the timing and synchronisation complexity that implies. Recall that DVI can have both an analog (VGA/DVI-A) and digital (DVI-D) signal in the same cable. They aren't independent; they share some pins and have the same timing. You could have made a CRT monitor that used DVI-D just by adding a DAC, though I'm not sure if any…

This also has side-channel implications, and is a reason why eDP is recommended in voting applications. https://www.eerstekamer.nl/nonav/overig/20160428/richtlijnen... >DisplayPort uses a scrambler as part of its line encoding in order to flatten the Fourier spectrum of its emissions and suppress spectral peaks caused by particular image contents. This reduces the chances of any particular image content causing a pro…

HDCP can't really be stripped, if it's on then something is an HDCP receiver. For v1.4 signals you can probably get something with the leaked key, but not for v2.2 as yet.

HDCP itself needs to be licensed in order to generate it, and that licence is only available to HDMI Adopter companies. However there is code to get some chipsets to turn it on: https://github.com/intel/hdcp

Grab it now before Intel deletes it completely.

HDCP is really a very ugly protocol designed just for anti-copying, I wouldn't build anything relying on it, and everything is harder with HDCP from an AV integration perspective. If you have long links that you want to secure, use something like SDVoE with encryption and authentication (bits are easily flipped in HDCP).

Re: Displayport: A Better Video Interface

#243

Post by bdavbdav »

nfriedly wrote: post #25

I'm annoyed nvidia for putting the current generation of HDMI on their recent GPUs, but leaving them with an outdated version of DisplayPort. For a long time, my advice to anyone was to always choose DisplayPort whenever it was an option. But now that has to have the caveat of "if you have a new high-end GPU and a fancy high refresh rate monitor, HDMI might actually be better for your situation"

I also noticed that many boards are 3xHDMI+1xDP now. My previous card was 3DP 1HDMI

Re: Displayport: A Better Video Interface

#244

Post by CyberDildonics »

bluedino wrote: post #109
BadBadJellyBean wrote: post #4

I just wish there was only one connector. Either HDMI or DP. I don't care.

Oh, but there's a third. MiniDP. I have a pile of useless cables/adapters now, since Apple started using them but replaced them with USB-C back in 2015.

Oh, but that's not a different video interface.

Re: Displayport: A Better Video Interface

#245

Post by thereddaikon »

MisterTea wrote: post #196
TazeTSchnitzel wrote: post #143

The amazing thing about DVI, and by extension HDMI, is that it's just VGA but digital, with all the timing and synchronisation complexity that implies. Recall that DVI can have both an analog (VGA/DVI-A) and digital (DVI-D) signal in the same cable. They aren't independent; they share some pins and have the same timing. You could have made a CRT monitor that used DVI-D just by adding a DAC, though I'm not sure if any…

> You could have made a CRT monitor that used DVI-D just by adding a DAC, though I'm not sure if anyone ever did. From memory IBM offered a crt with DVI.

Plenty did but they were usually DVI-A or DVI-I

Re: Displayport: A Better Video Interface

#246

Post by madars »

angry_octet wrote: post #242
madars wrote: post #200

Earlier quoted context omitted.

This also has side-channel implications, and is a reason why eDP is recommended in voting applications. https://www.eerstekamer.nl/nonav/overig/20160428/richtlijnen... >DisplayPort uses a scrambler as part of its line encoding in order to flatten the Fourier spectrum of its emissions and suppress spectral peaks caused by particular image contents. This reduces the chances of any particular image content causing a pro…

HDCP can't really be stripped, if it's on then something is an HDCP receiver. For v1.4 signals you can probably get something with the leaked key, but not for v2.2 as yet. HDCP itself needs to be licensed in order to generate it, and that licence is only available to HDMI Adopter companies. However there is code to get some chipsets to turn it on: https://github.com/intel/hdcp Grab it now before Intel deletes it comp…

There are devices that will give you HDCP 2.3->1.4 conversion for compatibility reasons (or maybe wink-wink reasons), and after that you can use a HDCP 1.4 stripper. There are also devices that will strip 2.2 outright (they are marketed as HDMI splitters but, oops, one of the two outputs has unencrypted signal, an honest mistake); not sure about 2.3 though. Completely agree that HDCP makes everything harder, but in this scenario it would also make attacker's job of descrambling the eavesdropped signal harder. And this is after they have overcome packetization and spread spectrum hurdles, which the paper suggests is very challenging to do, so would be a (hacky) defense-in-depth for DisplayPort. Even more important for HDMI/DVI which lacks the aforementioned hurdles.

Re: Displayport: A Better Video Interface

#247

Post by bdavbdav »

binkHN wrote: post #58

I didn’t realize Multi-Stream Transport (MST) requires OS support, and I was surprised to find out MacOS, with its great Thunderbolt support, does not support this. “Even” ChromeOS can do MST.

Yep. Super annoying. I have a Dell WD22TB4 which works great to drive 3 monitors for everything, except my Mac.

Re: Displayport: A Better Video Interface

#249

Post by stephenr »

tivert wrote: post #77

Are there any KVM switches that do Displayport well (i.e. where switching between inputs does not look like a display disconnect to the PC)? I'm still using HDMI because I like to share my home multi-monitor setup between my personal machine and my work laptop, and the KVM switches are able to fool the PCs into thinking the monitor are always connected. Years ago I tried a Displayport switch, but it could not -- I as…

The new Dell 6K has kvm (and PiP) functionality across its inputs, and it does appear from my modest use of this feature so far, that it works as you would want (ie it still thinks the display is connected, even when not showing that input)

Re: Displayport: A Better Video Interface

#250

Post by ben0x539 »

qwertox wrote: post #240

This is a really well written article. If you haven't bothered reading about DisplayPort because you knew VGA, somewhat knew DVI and thought that HDMI is the culmination of it all, where then DisplayPort is just some further kind of evolution, this article does a really good job at explaining how DP is very different and something new, something worth knowing about. The core sentence which made me actually read the a…

As a habitual comments skimmer, thanks for selling me on the article. :)
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