I made one for my computer monitor and it looks really impressive, particularly with games. Unfortunately it's much harder to do on a television DIY nowadays because you have to decode the HDMI signal in realtime, which isn't really feasible with a 4K picture on any remotely affordable FGPAs (AFAIK... I'd really like to hear if someone knows a part or combination of chips that would make this feasible at a hobbyist price, even hypothetically).

A computer monitor is easier, though, because you can run a program in the background that does screen capture.

The Hue software philips came out with for computers is a cheap way for people to get into this if they already have a computer, bridge, and some colored lights. https://www2.meethue.com/en-us/entertainment/hue-sync

I have a bunch of Hue devices myself, but I wouldn't exactly call it "cheap" considering how much the colored bulbs cost. You can build your own with a cheap Arduino clone and some addressable RGB LEDs for well under $20.

In addition, Hue Sync is kinda different. To me a proper ambilight goes around the edge of a display to cast light on a wall with a decent resolution (20ish or more LEDs), while Sync is more for a few bulbs and synchronizing the room lights. You can get kind of a similar effect with Sync and a couple bulbs behind the screen but it's just not as impressive.

Hence my caveat about already having said expensive bulbs. The possibility exists that someone could to real time whole room color effects right now and they just didn't know it.

If you want actual ambilight tech hue is definitely not directly analogous and not cheap either.

Phillips sells hue led strips now, wouldn't that work with hue sync?

The Hue strips aren't addressable so all the LEDs are set to the same color.

I came across Lightberry [1] recently that claims they can do 4k @ 60 Hz from an HDMI signal, and is also HDCP compliant.

This talks to a Raspberry Pi using USB 2, and on their site [2], it talks about using the UTV007 [3] and STK1160 [4] chips, both of which are only 720x480px @ 30fps. As you really don't need high resolution for the LED lighting, what they must be doing is using an HDMI splitter and then converting to a lower quality signal, and then capturing/sampling that. Normally HDMI doesn't allow this but it's probably not too hard to find splitters that silently do this anyway.

In fact, here's a write-up [5] on using the "HD Fury Linker" [6] to basically upgrade the "Lightberry HD" to work with 4k. HD Fury makes some interesting products to manipulate the HDMI handshake an EDID [7] and an HDMI splitter that has HDCP decryption/encryption and "comes with USB upgradable firmware that allow you to unleash furious features" [8].

The last time I looked at this was about 10 years ago and I remember being put off by the compromises and complexity the HDMI signal path issues caused. Looks like that is no longer an issue (provided you are willing to pay for the gear).

[1] https://lightberry.eu

[2] https://lightberry.eu/getting-started/#grabberAccordion

[3] https://www.linuxtv.org/wiki/index.php/Easycap#USBTV007_Easy...

[4] https://www.linuxtv.org/wiki/index.php/Stk1160_based_USB_2.0...

[5] http://www.chewie.co.uk/general/how-to-get-lightberry-hd-to-...

[6] https://hdfury.com/product/linker-4k60-444-600mhz-scaler/

[7] https://hdfury.com/product/dr-hdmi/

[8] https://hdfury.com/product/splitter-4k/

Yeah, I have thought some sort of downsampling chip was probably the way to go, but I'm not that familiar with products in that area. This is exactly why I am asking here, thanks!

You don't have to decode a full frame. Just throw away the middle you don't need. Skipping every other frame would also buy time for a slower decoder.

It's not so much the decoding and memory as it is that the timing of the HDMI signal waveform at 4K/60fps is a bit too fast to read any portion of with an affordable FPGA. There are FPGAs with specialized DSP hardware that can probably do it, but the ones I know of require pricey IP core licenses and the chips themselves aren't terribly affordable.

That's kinda what I'm asking about here, if there is a something like a specialized chip that can be used to capture single frames from an HDMI stream to act as a buffer, because yeah obviously you don't need most of the data and you only really need to update at a few Hz.

The other option I've thought of is a chip to downsample the signal, as there are plenty of cheap FPGAs or even micros that can handle resolutions below 1080p. Again, I'm pretty sure such chips exist but I don't really know of them because this is just something I am interested in for fun.

A Xilinx one with transceivers should be able to do it though. Yes, not cheap as such, but oh well. Depending on resolution, a 3 or 5GHz transceiver chip from lattice should be reasonably cheap, and IIRCV they have special HDMI chips.

Ambilight is nice because it allows you to play / watch in a dark room. In my case at least, I don't get eye fatigue as it lights up the room enough to be comfortable.