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Comment by jagrsw | Hacker News Reader

In the "old times" a video mode descriptor included things like "front porch", "sync width" and similar unpleasantries. I believe they're still used with DP/HDMI, as it's possible to play with "modelines" in Linux and adjust those params.

My naive understanding is that it's a legacy thing from CRT times, where there was a need to allow for the electron gun to adjust itself for a new line/frame.

Do those terms have still meaning in HDMI/DP/LCDs times, or they're preserved but serve no purpose now?

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The only thing that still matters are: the vertical back porch (it matters for variable refresh rate, too high and it will increase latency too much), the total vertical blank (it must be high enough to give the source to time to reconfigure itself to go to power savings mode) and horizontal blank (it must be high enough to insert HDCP information and audio samples.)

Sync polarities, sync width, horizontal front and back porch are usually ignored by monitors.

Overscan/underscan still has a meaning even in the HDMI age, as do different black/white level limits, that all originate from the CRT era and its need to account for mis-aligned beams [1]. You may notice it when you plug in a PC into a TV's HDMI and don't see the title or task bar, or blacks look weirdly "off". If you ever encounter that, enable a setting commonly known as "game mode", and also check for color profiles as some TVs don't tie color space / temperature to game vs TV mode.

Bonus points: add SDI or scalers to the mix, now that's real fun to troubleshoot. More bonus points: try to troubleshoot this with just a Blackmagic VideoAssist... awesome things in general but it's completely beyond me why they don't have an ability to show basic information about the incoming signal. JFC.

[1] https://en.wikipedia.org/wiki/Safe_area_(television)

I've seen TV overscan settings be in menus like "Size", "Aspect Ratio", and "Scan", but never "Game Mode". Which manufacturers call it that?

In my experience game modes are usually focused on lowering display latency at the expense of processing quality.

CRT tvs with dvi-d and hdmi exist, where I'd imagine all those things in the mode line are still useful. I gather DisplayPort signaling is significantly different, however.

I had a WEGA driven by HDMI and overscan was important. The TV didn't fake it, the pixels were drawn outside the bezel, and they could be brought in by adjusting the picture. However, they were very distorted. Everything was fine when compensated for overscan, but some things like Amazon video's menu used every pixel and were cropped.

I had never thought about overscan until I used that TV.

The innovation of DP is that it's the first video standard to virtualize the physical interface of video. All standards before it directly represented the video timing on the physical layer (e.g. DVI/HDMI bit-clock = bit-depth × pixel clock). DP takes the same video signal (including blanking intervals) and chops it up into packets with some stuffing so as to not change average timing, then transmits them over fixed-rate physical links.

I recently managed to overclock a pair of xreal air AR glasses (USB-C DP altmode based) to 90hz using custom modelines, so it's still relevant.

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