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A comment on HDMI Forum Rejects Open-Source HDMI 2.1 Driver Support Sought by AMD. Parent comment

Re:HDMI Forum Rejects Open-Source HDMI 2.1 Driver Support So... by tim-- on Wednesday February 28, 2024 @05:05PM (#39544080)
From what I understand (and I could be very wrong here) the biggest issue here is simply the amount of memory that is required in order to keep a copy of the current frame from a HDMI signal, and the fact that to modify anything in the HDMI signal, you need to decrypt (if watching a HDCP protected stream), decode each frame, and then finally re-encrypt the HDMI signal.

I was looking into what would be necessary to build a HDMI switch that allowed for seamless switching of video between different inputs, and basically there was no hardware for it. The closest chips that I could find was Analog Devices' ADV7626 and Lattice's SiI9777S.

Lattice CP9777 might be worth having a look at if you can understand anything about the datasheet :)

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Re:HDMI Forum Rejects Open-Source HDMI 2.1 Driver Support So... by 4rt on Wednesday February 28, 2024 @05:32PM (#39544337)
As far as I can see there's no need to re-encrypt the signal - just leave it as a non-HDCP stream?

There are HDMI splitters which silently strip HDCP to output to two screens at once - they don't advertise this feature but they do it anyway in order to function. In order to achieve the overlay you'd just need one of these and then a non-HDCP-aware overlay apparatus before the display.

https://www.reddit.com/r/VIDEOENGINEERING/comments/xme482/hd...

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Re:HDMI Forum Rejects Open-Source HDMI 2.1 Driver Support So... by charcircuit on Wednesday February 28, 2024 @08:39PM (#39545681)
You won't be able to get keys for HDCP if your device isn't compliant
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Re:HDMI Forum Rejects Open-Source HDMI 2.1 Driver Support So... by mrandish on Wednesday February 28, 2024 @10:24PM (#39546119)
I believe these kind of cheap, no-name converter/adapter boxes use leaked HDCP keys.
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Re:HDMI Forum Rejects Open-Source HDMI 2.1 Driver Support So... by userbinator on Wednesday February 28, 2024 @11:06PM (#39546307)
The master key was cracked long ago. You can generate as many of your own unique keys as you want.
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Re:HDMI Forum Rejects Open-Source HDMI 2.1 Driver Support So... by charcircuit on Thursday February 29, 2024 @12:18AM (#39546608)
This only works for old HDCP versions though
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Re:HDMI Forum Rejects Open-Source HDMI 2.1 Driver Support So... by mjevans on Wednesday February 28, 2024 @05:41PM (#39544419)
It would be a LOT more seamless if the output didn't have any HDCP to re-synchronize. Though the different frame timings (gen-lock is a term you want to search for) between the inputs and outputs so such a system might introduce presentation latency which would have to be accounted for in the audio streams.
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