undefined | Better HN

0 pointsjwells892y ago0 comments

It’s niche I’ll admit, but a while back the lack of support for DisplayPort in home theater equipment bit me because I had an Oculus Rift (original) hooked up to the same machine, using the only HDMI output on the computer’s GPU which meant hooking it up to the TV (through a receiver) required a DisplayPort → HDMI adapter.

Thing is, DP → HDMI adapters all suck when you’re using them to send anything but a basic 1080p picture. They nearly all fail or struggle with uncompressed 4K. I tried several different cables and adapters and despite marketing claims, they all had trouble. The best was one that was externally powered via USB, but even it exhibited quirks.

I no longer have the Rift hooked up to that machine which freed its HDMI port up, but I too wish TVs and receivers had even just one DisplayPort.

0 comments

jasomill2y ago

At least a few active DP → HDMI 2.0 are okay at 4kp60. For example, these[1][2] do 4:4:4/RGB 4kp60 fine, though they're limited by HDMI 2.0 to 8 bits per color channel at 4kp60 (higher bit depths work fine at lower resolutions and frequencies, or with chroma subsampling).

In my testing (several years ago), at least half a dozen other similarly-priced DP → HDMI 2.0 adapters purchased from Amazon were limited to chroma subsampled output (4:2:2 or 4:2:0) at 4kp60, which is obviously unacceptable for desktop use, so I do see your point.

I've used the linked adapters successfully now for several years with both a 2013 Mac Pro and a pair of DP-only AMD GPUs (WX 3200 and WX 4100), all connected to a 2019 LG TV, and, while testing, confirmed all claimed signal outputs using an HDFury Vertex.

[1] https://www.amazon.com/dp/B00S0BWR2K

[2] https://www.amazon.com/dp/B00S0C7QO8

iforgotpassword2y ago

It's complicated, but the tldr is: use a DP++ type 2 adapter that advertises 4k compat.

DP++ adapters tell the GPU to output an HDMI signal instead (DP is an entirely different protocol), and then just level-shift the signal. Type 1 adapters are limited to i-forgot-how-many MHz which means no more than 1080p60. Type 2 adapters contain a tiny 256 byte rom that tells the GPU its maximum supported bandwidth.

Other adapters are active, they convert the signal and thus add latency, and often need external power so can get quite hot.

jasomill2y ago

I haven't noticed any perceptible latency from any active DP → HDMI I've used, and I'd honestly be surprised to see any inexpensive active DP → HDMI adapter introducing latency, if only because doing so would require a frame buffer, which drives up costs.

What I have seen is DP → HDMI adapters that only support chroma subsampled pixel formats at 4kp60, and TVs that introduce many frame times' worth of latency due to various post-processing effects.

My hunch is as follows: given that consumer video devices (DVD/Blu-ray, set top box) almost exclusively output chroma-subsampled 4:2:2/4:2:0 YCbCr formats, TV post-processing pipelines may only support these formats, causing RGB (and possibly 4:4:4 YCbCr) signals to bypass post-processing, similar to the "PC" or "Game" modes present on some TVs that do the same.

In other words, if adapter → 4:2:2/4:2:0 and 4:2:2/4:2:0 → TV post-processing → latency, then adapter → latency, even if the adapter itself introduces no significant latency.

If I'm correct, the solution is an adapter which supports RGB output at the desired resolutions and frame rates and/or a TV with a PC/Game mode that bypasses post-processing for all source types, both of which are highly desirable for "monitor" use in any case.

j / k navigate · click thread line to collapse

0 pointsjwells892y ago0 comments

I no longer have the Rift hooked up to that machine which freed its HDMI port up, but I too wish TVs and receivers had even just one DisplayPort.

0 comments

jasomill2y ago

[1] https://www.amazon.com/dp/B00S0BWR2K

[2] https://www.amazon.com/dp/B00S0C7QO8

iforgotpassword2y ago

It's complicated, but the tldr is: use a DP++ type 2 adapter that advertises 4k compat.

Other adapters are active, they convert the signal and thus add latency, and often need external power so can get quite hot.

jasomill2y ago

In other words, if adapter → 4:2:2/4:2:0 and 4:2:2/4:2:0 → TV post-processing → latency, then adapter → latency, even if the adapter itself introduces no significant latency.

j / k navigate · click thread line to collapse