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Comment by seiferteric | Hacker News Reader

I wish monitors in general had better (and open) firmware. It would be really cool if for example I could have my laptop plugged into my desktop's monitor and have it show up as a "window" on my desktop. All it would take would be for some simple driver on my desktop to tell the monitor where to draw the image when I moved the window around. Basically a better version of the mostly useless PiP feature my monitor already has.

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As with many things, this comes back to DRM. HDCP in specific.

Monitors are generally connected through DisplayPort or Thunderbolt, not HDMI, so there's no reason for HDCP to enter here. The card in question does have a HDCP output, but advanced features are only available through DisplayPort.

> Monitors are generally connected through DisplayPort or Thunderbolt, not HDMI, so there's no reason for HDCP to enter here.

HDCP runs over DP and Thunderbolt. But derefr's discussion above is accurate.

It might surprise you that most monitors out there, especially the cheap garbage ones from Amazon/Walmart that most consumers have in their homes, are connected via HDMI.

As someone running their monitor over HDMI, this is news to me. If it gives the resolution and framerate of the monitor, what's the difference if it's HDMI or DisplayPort?

For you as an end consumer nothing if bandwidth is enough with either cabke, but techies like us will be sticklers that one is more open than the other, not bound by royalties and such.

Displayport usually has something like 50 % higher bandwidth compared to the HDMI standard of the same vintage. Which makes sense, since home video folks are fine with like 15 pictures per second and 4:0:0 chroma subsampling, but that doesn't really work for computers...

That, and some video cards support higher resolutions over DisplayPort. For example, while my 2013 Mac Pro has both HDMI and Thuderbolt/Mini DisplayPort outputs, the only way to get 2160p60 HDMI output (without chroma subsampling) is via a DisplayPort-to-HDMI 2.x adapter (and I had to try about half a dozen different adapters before I found one that does this correctly).

Displayport used to be much better but now they both cover virtually everyones needs. Now the main difference is HDMI has a licensing fee. Some major TV companies are in the org so they don't have to pay it which is why TVs always use HDMI and GPUs usually have more displayport because those companies have to pay for hdmi.

In this particular case, no, as the image wouldn't be being sent into the PC to render in its framebuffer; but rather the PC would just be drawing an empty window, and reporting the geometry of that window to the monitor. The monitor, with two HDMI leads plugged in, would be responsible for compositing the inputs together, according to the geometry the PC reported, but all internal to itself.

That's how hardware-accelerated video decoding used to work in Windows XP days IIRC (before GPU-based desktop composition), the video player would be a blank black square and the GPU would be told to draw the video on those coordinates.

Because of how it was implemented, you could drag VLC around while the video was playing and the video would stay "behind" everything, with the VLC window acting as a "hole" through which you could see it. (So you could move the window to the left and see half a black square on the left, and the left-most half of the video on the right)

Nowadays with desktop composition AKA DWM, Windows just makes sure to black out DRM content from any frames/video it sends to an app requesting to capture the screen, making sure to send the video-including composed desktop only to the display. (And if you have some GPU recording software like NVIDIA ShadowPlay, it switches off when DRM content starts playing) You can see it in action with the Netflix UWP app. Of course, a bunch of DRM-respecting software -- like Netflix in Google Chrome -- doesn't really follow that spec and can still be screenshot/video captured like any app.

I found it odd that even Disney Plus - which I heard had the highest level security of Widevine enabled, can be screen recorded.

It provides lower resolution content to those devices, capping at 720p.

Which is the same as Netflix effectively, Netflix just provides higher to PCs when they can block screen recording entirely. Disney might eventually I guess.

This isn't a firmware issue, because enabling this would require adding the hardware to the scaler ASIC to actually process multiple video streams, and to increase the buffer size and bandwidth n-fold so that it can synchronize and composite the unsynced video sources (also introducing 1+ frames of latency).

The GP was assuming a scaler that already supported a Picture-in-Picture or split-screen feature—as many modern monitors do!

The problem—and it is purely a firmware problem—is that all such monitors make this kind of support "dumb", with hardcoded geometry (i.e. split-screen as exactly halving or quartering the screen; PiP as putting one input in an box that composites over exactly the upper-left quarter of the lower-right quadrant of the screen.)

There's nothing in the scaler ASIC that particularly benefits from these numbers being hardcoded, such that its job would be any more complex if they were controllable via machine-registers POKEable using HDMI-CEC commands.

I think they mean DRM is the reason we can't have open firmware. Not that DRM is the reason we can't have sophisticated PiP features.

It would be cool if the entire Onscreen Menu would be available as api. I hate using it to switch between inputs or to turn of my second monitor.

Look into DCC/CI, it's possible your monitor supports that already.

Just use remote control software to connect from one computer to the other and display it as a window.

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