I've always believed - and explained to customers - that HDCP, when implemented - is a two-way, encrypted handshake between source and display. Once HDCP was implemented, utilizing a source at 720P or 1080i on multiple displays simultaneously would be impossible because the protocol doesn't support multiple handshakes (let alone a DA or Matrix switcher supporting 3 displays sending the signals back to the same source gear.)

I've spoken to a couple of other designers who have a different understanding - that using DA's can "multiply" the availability of the source. At at least one install (commercial), this was confirmed by a fairly well know HDCP licensee.

But when I look at the protocol (see page 15 of [Link: digital-cp.com]) I really can't believe that more than one display can participate in the key exchange...even if the protocol somewhere supports it, wouldn't it be like hooking up multiple pieces of gear to same RS-232 recieve pin? It would just screw up the communications....

There does seem to be a repeater protocol that might be able to be implemented however this would require that the matrix switchers get *much* smarter than they currently are....

Is this other folks understanding - that HDCP = no multi-set distribution - or is there a work-around I'm missing.

-Aaron

Aaron, You pose an interesting question. I had not considered this issue with HDCP. I suspect that those manufacturers that are implementing HDMI with HDCP would be able to answer this for us. I will let you know if I can find any information on this. Are there any manufacturers frequenting this format that are willing to chime in on this?

Aaron,

Do a search at AVS forum on the name Amillians (I hope that's the right spelling). Then post the question there or send him a forum message. He has done a tremendous amount of research on the issue and should be able to give you an answer.

However, companies like Geffen are selling HDCP compliant video splitters that work

Aaron,
You have a pretty good understanding of HDCP already, and your assumptions are correct. However your other designer friends are also correct.

It is possible to make a DA or matrix switch that will allow for multiple sources and multiple displays, all supporting HDCP. In order to do that, each input DVI/HDMI receiver chip must understand and decrypt HDCP. Then the distribution and routing can take place inside the switch unencrypted. Final stage at the output is the DVI/HDMI transmitter chip that supports HDCP, and will encrypt the data on it's way out. So really you have more than one seperate HDCP session going on, the ones between the source devices and the switch, and others between the switch and the displays.

If you need to switch multiple sources into one display, you can sort of cheat the system by not decrypting the data, and letting the source talk directly to the display. In that case the source and display have no idea there is a 'man in the middle', and it is only a single HDCP conversation. That is the method used by most DVI switches on the market that support HDCP.

I beleive Gefen has obtained the proper license from HDCP, so they can now decrypt that video, and do things like a DA that supports HDCP on all outputs.