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I have two 4K monitors which I hook up to my laptop for video editing.

I got a Docking Station from i-tec which is advertised as "USB 3.0 / USB-C / Thunderbolt 3" and "up to 2x 4k@60Hz". The monitors are connected to the dock with DP cables.

In real-world conditions, I experience stuttering on the external displays, especially for full-screen videos. The stuttering will stop if I connect only one monitor, rather than two.

Digging into the issue, I found out that the Docking station maxes out at 5Gbps (so much for the "Thunderbolt"...). Evidently, it uses DisplayLink to communicate between PC and Dock, and the Dock will convert the video-signal back to DP before sending it to the monitors.

DisplayLink does not officially publish any data rates, but basically says "it depends on what you're doing". I understand it creates a virtual display buffer in RAM, then compresses the video signal and sends only the data which differs between consequent frames.

I can understand that this will deliver well for mouse cursor movements or text editing, but I can't get how two 18Gbps video streams (approx data rate for 4K60Hz) possibly could be compressed and sent over the same 5Gbps line which also guarantees my LAN connection, Mouse and possibly 1-2 external HDD's.

  • So, did I fall for a marketing stunt by buying that Docking station?
  • Does any one manage to get smooth video display over a similar setup?
  • In order to get smooth playback on the two monitors, should I go directly for a TB 3.0 dock, which my PC would support (but which costs me 3-4x the money) ?

My system is a Lenovo Yoga C940-15IRH. i7-9750H / 16GB Ram / NVidia GTX 1650 Max-Q. The monitors are Dell U2720q

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  • Are you using proxy video? I can't imagine doing 4k video edits on a laptop, tbh, & I'm not sure it's the dock box to blame.
    – Tetsujin
    Commented Feb 7, 2022 at 17:18
  • These docks generally have lower output when using USB-3 rather than USB-C, but the answer is yes, you can still push 2x4k@60 through a USB-3 connection. USB-C can go higher.
    – Cpt.Whale
    Commented Feb 7, 2022 at 17:44
  • That said, displaylink has to encode all of that on the cpu. If you're already doing fairly intense video work, then you may get pretty terrible performance overall. Try plugging one of your monitors directly into the laptop with a thunderbolt-to-dp cable, and see if performance improves on the dock monitor
    – Cpt.Whale
    Commented Feb 7, 2022 at 17:49
  • @Cpt.Whale Thank you. Yes, I've got that in the meanwhile by browsing through other threads. It's bascally just good for an office setup, but not for multimedia
    – 1NN
    Commented Feb 7, 2022 at 18:04
  • @Tetsujin I find my system works well for Premiere Pro, for up to two 4k video sources, plus basic graphics overlays. It works quite well with internal monitor plus one external monitor. It gets a pain when applying multiple effects. That said, for more complex projects I'm using proxies. I wouldn't use this system for daily video editing, though.
    – 1NN
    Commented Feb 7, 2022 at 18:37

1 Answer 1

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I found the reply in a thread of the dell support forum, for a similar product:

It’s because the [docking station] use DisplayLink rather than tapping into native GPU outputs. DisplayLink uses a driver to have the CPU and GPU compress video for transmission as regular USB traffic, and then a chip in the dock decompresses it and transmits it to the displays. That’s why you’re seeing all that CPU activity and horrible performance. DisplayLink is fine for basic productivity tasks, but when lots of the display area is changing at once, such as when gaming or watching full screen video, that’s a lot more work to do, so your CPU gets busy and you can end up with jerky/judder-y video.

[...]

You need a dock that taps into native GPU outputs.

So, basically, yes, this needs a TB 3.0 dock.

Furthermore:

It’s really meant as a business dock for use cases involving email and spreadsheets. Its main value proposition is that it can be used with both USB-C and USB-A systems, which means companies that currently have a mixture of older systems with traditional docking connectors and newer systems with USB-C/TB3 can standardize on this one dock model. That’s especially useful for companies with “hotel desk” setups.

So, I can't say it's a "marketing stunt", as it can in some situations be a valid solution. But it's just not a good solution for any multimedia setup.

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