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127: HDMI’s Magic Number
He asks, "Is there any truth to there being a limit on the number of displays one system can offer?"
The answer (yet again) is both yes and no.
When it comes to hardware, there is no limit. But there's a software side to keep in mind, and that's where the number 127 comes in.
As many of you know, today's video systems incorporate copy protection from the good folks at Digital Content Protection LLC.
It involves HDCP (high-bandwidth digital content protection) encryption keys in order for products to talk to one another. When a system is connected, all the keys eventually have to end up at the source, which has the potential to hold 127 keys.
Many source products limit the number of downstream device keys its firmware can read, store and process. An example would be a source, an A/V receiver and a display (making a total of two downstream keys).
We have seen products come in with as few as three keys, which is not enough to handle some distribution. This can sting you. So be aware of source products' key capability.
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5 Comments (displayed in order by date/time)
gefen said they were making a list of components with lots of keys. the larger issue with HDMI (beside sucking a lot) is distributing the video via HDMI and the audio separately. If you can strip the audio out of the HDMI (or come digital from the source) you still have to worry about audio delay. HDMI is not really made for distributed systems. I can’t wait until it is totally replaced with IP video dist.
Lee:
To the best of my knowledge no.
Send me an email Lee.
Jeff
Hi Jeff,
I’ve heard from a few installers that they’ve seen content itself dictate how many displays/devices it can be output to simultaneously. Is there any merit to this? Have you seen/heard anything similar?
Probably the worst devices out on the market are the current Panasonic Blu-Ray players. These devices only support 3 keys which means you can only use them with basic type system configurations using only HDMI cables and with surround sound receiver and display device. These Panasonic Blu-Ray players will not work in a system where you have HDMI baluns in the video path (doesn’t matter on the brand HDMI balun) or any other device that needs a HDMI key.
Great column Jeff. Has there been any action at all to motivate manufacturers to list in the specs the number of keys their device will accept?