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We have a conference room setup that uses a ceiling-mounted projector, a computer and possible inputs from travelling laptops. Part of the setup involves switching between several devices using HDMI to output to the projector.

So we acquired a 5x1 HDMI switch.

However, our AV guy says the switch only has one license for the use of HDMI - which means that every time you connect or disconnect one of the HDMI sources, the device has to rescan everything and re-register (he says "handshake") everything before it can connect to the new item.

He says that we need a switch that keeps all the devices registered so they don't have to be rescanned every time.

Now I don't want to go on a wild-google-chase to find this thing if it doesn't exist. Can someone confirm that this thing does, indeed, exist? What do you call it?

I'm not asking for a product reference - I'm asking whether there is such a thing and what terminology I would use in order to find it.

bgmCoder
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    Can you explain what the issue is with the switch you bought? Is it not working how you expected? What is that issue? – Keltari Feb 12 '13 at 20:45
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    Why not ask the "AV guy" to produce one for you, or at least help you find one? – Ƭᴇcʜιᴇ007 Feb 12 '13 at 20:47
  • If the AV guy could do this for me, I wouldn't be here asking. He's not really an employee - just a servicing agent for one of the devices. – bgmCoder Feb 12 '13 at 22:05
  • @Keltari I did say what is wrong with the current switch - it has to re-register all of the devices every time something is connected or disconnected. I think I need a switch that keeps them all registered. – bgmCoder Feb 12 '13 at 22:08

2 Answers2

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You havent explained what the problem is, you have only stated what it is you are trying to "fix."

However, it sounds like your "AV guy" doesnt know what hes talking about. The switch is not the problem. The switch just sits there and passes data back and forth. Its completely passive.

HDMI has the ability to protect data from piracy. It uses high-bandwidth digital copy protection (HDCP) to accomplish this. HDCP is an authentication protocol. Basically, each home-theater device or computer graphics card has identification data and encryption data stored on its extended display identification data (EDID) chip. The source device, such as a your computer and laptops, checks the authentication key of the receiving device/ In your case, its the projector. If both keys check out, the sending device moves on to the next step. It generates a new key and shares it with the receiving device. In other words, it creates a shared secret.

This whole process, known as a handshake, takes place almost instantaneously.

The source device encodes its information using the key it generated it. The receiving device decodes it using the same information. If an unauthorized device tries to intercept the data, the source device stops transmitting. It also makes sure that the key hasn't changed and that the system is still secure every few minutes.

You should have no issues with the set up you described.

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Keltari
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  • I think that what he mean is that the switch, in order to work optimally, needs to be able to remember that the keys were already investigated, so it doesn't have to check again. The switch I have has to reinvestigate every device each time a new one is added (I think). Have you ever heard of this? – bgmCoder Feb 13 '13 at 05:47
  • My problem is that I don't know how to find what I am looking for. – bgmCoder Feb 13 '13 at 17:01
  • We are having a disconnect here. You have a projector, computer, laptops, and a HDMI switch. Based on the set up you have, everything should be fine. Yet, you seem to insist you need a different HDMI switch. You havent explained why you need another switch and why the equipment you have is not working. – Keltari Feb 13 '13 at 17:08
  • Yes, I do have a problem, but that isn't the question I asked. If you are asking for my underlying problem, I'd have to ask a whole set of questions requiring a set of answers to match, and may not be able to ask a good question - which risks me getting negative votes or my question closed. So I've asked a direct question to get a specific answer, and based on the findings, I can narrow down my problem and ask a separate question that is more focused. Am I wrong to think this way? – bgmCoder Feb 13 '13 at 17:19
  • well as you can see, you arent getting what you need by being vague. If you have a specific problem, ask a specific question. – Keltari Feb 13 '13 at 17:23
  • I really thought I did ask a specific question: Is there a Such Thing as a Multi-Licensed Multi-Channel HDMI Switch? "I'm asking whether there is such a thing and what terminology I would use in order to find it."

    How much more specific can that be? Am I wrong to expect someone to answer that?

     – bgmCoder Feb 13 '13 at 17:33
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    there is no such thing as a "licensed" HDMI switch – Keltari Feb 13 '13 at 17:36
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Actually, this kind of HDMI switch (that is "always negotiated") does exist. This page has a very nice article about HDMI and the troubles of "handshaking":

Since we do power-off displays and source devices most issues occur when these devices are powered on again to re-negotiate the HDCP handshake between source and display.

...Some displays may also re-negotiate the handshake when swopping to another input e.g. AV1 ,AV2 or another HDMI Port (wait 10 seconds) and swopping back to correct HDMI Input via remote control.

Some devices such as switches and HDMI Switches / Combo splitters also allow for HDMI handshake re-authentication by switching from one input to another and back to the input having HDCP handshaking issues.

The "thing" that keeps the "handshake" open is called EDID - that is, Extended Display Information Data. See here:

Extron HDMI matrix switchers also feature Key Minder®, an Extron-exclusive technology that continuously verifies HDCP compliance for quick, reliable switching.

Octava has this to say about EDID:

-EDID Management: EDID is an acronym for Extended Display Information Data. EDID was originally implemented by computer monitors to communicate its display capabilities to the video card so a compatible video resolution could be negotiated. EDID is also used by HD Displays via HDMI to identify the HDTV display and audio capabilities to the connected video source. Basic HDMI switches with single output simply pass the EDID directly from the display to the source. For multiple output devices such as a HDMI distribution amp, or matrix switchs, a method for customizing or managing EDID is recommended. EDID Management allows the user to manually select the desired EDID in order to properly operate a multi- display system which may include multiple displays and audio receivers each with differing capability.

Wikipedia says:

EDID ... It is what enables a modern personal computer to know what kinds of monitors are connected to it.

Here is an example of an HDMI Switch that uses EDID:

This 1X4 HDMI Splitter w/User Adjustable EDID chip-set includes a chip to makes sure the sound and the picture are in sync and no delays occur between them.

However, it seems that the ports have nothing to do with licenses, really, however, the switch must be HDCP compliant, which is where the notion of "license" may have come from.

The reason it seems like the devices have to "re-register" is because the switch does not maintain continuous EDID communication with the sources. To have the seamless integration, the switch has to have a EDID control inside which can "know" that devices are still connected by detecting their display settings.

bgmCoder
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