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Random instant GFX issues (wavy pixels) which occasionally followed by instant No Signal black screen (encoder on the pi issue) #815

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opened 2026-02-20 14:06:50 -05:00 by deekerman · 4 comments

deekerman commented

2026-02-20 14:06:50 -05:00

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Originally created by @plia7 on GitHub (Jan 22, 2024).

Originally assigned to: @mdevaev on GitHub.

Describe the bug
I have a Dell laptop which only has usb c ports, so in order for me to connect pikvm to it, I connected an adapter that has hdmi ports:
"Docking Station USB C to Dual HDMI Adapter, MOKiN USB C Hub Dual HDMI Monitors for Windows,USB C Adapter with Dual HDMI,3 USB Port,PD Compatible for Dell XPS 13/15, Lenovo Yoga,etc"
https://www.amazon.com/dp/B08CRCRPCJ

https://www.amazon.de/-/en/dp/B0CLNCJPCG
I'm getting random instant GFX issues (wavy pixels) which occasionally followed by instant No Signal black screen. This is the sequence when it happens together:
[normal screen] [instant wavy pixels somewhere on the screen] [instant no signal black screen] [normal screen].

To Reproduce
Steps to reproduce the behavior, like:

Connect to pikvm (from internal or external network, doesn't matter, the issue occurs in both).
Stay connected and use it for few hours.

Expected behavior
Being able to stay connected and use it for few hours without any random instant GFX issues (wavy pixels) which occasionally followed by instant No Signal black screen interruptions assuming stable internet connection.

Actual behavior
Random instant GFX issues (wavy pixels) which occasionally followed by instant No Signal black screen starts appearing after some time (could be after minutes or hours) where it works fine until that point. It could happen again randomly after some time (could be minutes or hours). Note that I had sessions where the issue could get so severe it would be happening like every 15-30seconds (which is not that random anymore).

These are my runtime settings:

Some discord channel members said about this issue
"if it goes to uncanny valley, it's the encoder on the pi, not sure why but it is. and I've seen that kind of behavior before."
"I wouldn't think the signals would get wavy there because it's digital until it gets to the Toshiba chip but it is parallel digital signals..."
"it's a digital signal, like packets over an ethernet cable, if there's disturbance the internet doesn't get wavy"
"the Pi does signal processing on the images coming in "
"It's kind of artistic, though I agree it's not the expected look."
"no signal processing should occur until it reaches the decoder chip on the Pi 4. In theory at least."
Including support members said about this issue
"we have seen some odd behavior from port expanders"
"no signal is the one I have seen and saw reported"
"We have heard about odd behaviors from port expanders - mainly a No Signal as a result of pikvm not knowing what the target resolution is so it keeps trying different resolutions which would explain the random like No Signals you have seen"

Things I've tried to resolve the issue

Change setting to gop 0 or play with kbps/bitrate.
switch hdmi cables (used both the hdmi cable that comes with pikvm from pi shops and amazon basics hdmi cable).
I thought initially that ezcoo is causing it, so I connected the pikvm directly to the adapter without ezcoo.
updated pikvm software to the latest version.
Made sure target machine advanced display settings it shows 1080p at 50 hz resolution.

Logs:
*I'll try to get the logs after the issue occurs next time to see if there is anything about it in the log that could be useful (or please let me know what kind of logs do you need).

Screenshots/Videos
This is what the gfx issue (wavy pixels) look like (note how towards the end of the video a large portion of the pixels are "melting" and going out of order):

https://github.com/pikvm/pikvm/assets/134864072/9a289305-d8f5-4191-9803-fd0a75eb2d3c

Wavy pixels:

Note that it's happening in different areas in different programs, windows, etc.
It causes some letters sentences to tilt like a wave in some area / lines of the screen.

And this is the regular display how it should be:

Occasionally it's followed by instant No Signal black screen (I found this picture on google images for illustration purposes, I believe the "no signal" letters are in yellow in the pikvm version):

Desktop (please complete the following information):

OS: [e.g. iOS]
Windows 11
Browser [e.g. chrome, safari]
Chrome 120.0.6099.225 (Official Build) (64-bit) (cohort: Stable)
Version [e.g. 22]
VNC client (if used)

PiKVM info:

Raspberry Pi board version [e.g. RPi 4]
PiKVM v3 Pre-Assembled
PiKVM platform [e.g. v2-hdmi]
Video capture type [e.g. CSI bridge]
KVMD version: pacman -Q | grep kvmd
kvmd 3.293-1
kvmd-fan 0.29-1
kvmd-oled 0.26-1
kvmd-platform-v3-hdmi-rpi4 3.293-1
kvmd-webterm 0.48-1
uStreamer version: pacman -Q | grep ustreamer
ustreamer 5.48-2
Linux kernel: uname -a
Linux pikvm 6.1.61-1-rpi-ARCH #1 SMP Fri Nov 3 20:48:52 MSK 2023 armv7l GNU/Linux

Additional context
I tried to connect a physical Dell monitor to the MOKiN adapter hdmi port - And I haven't observed the reported issues happening. So what is it about the encoder on the pi that's randomly messing up the hdmi transmission causing instant wavy pixels and/or no signal black screen - I don't think the adapter used should affect how pikvm shows the signal (especially if the adapter works fine with a physical monitor). Note: I have two PiKVMs and it happened with both.

Originally created by @plia7 on GitHub (Jan 22, 2024). Originally assigned to: @mdevaev on GitHub. **Describe the bug** I have a Dell laptop which only has usb c ports, so in order for me to connect pikvm to it, I connected an adapter that has hdmi ports: "Docking Station USB C to Dual HDMI Adapter, MOKiN USB C Hub Dual HDMI Monitors for Windows,USB C Adapter with Dual HDMI,3 USB Port,PD Compatible for Dell XPS 13/15, Lenovo Yoga,etc" https://www.amazon.com/dp/B08CRCRPCJ https://www.amazon.de/-/en/dp/B0CLNCJPCG I'm getting random instant GFX issues (wavy pixels) which occasionally followed by instant No Signal black screen. This is the sequence when it happens together: [normal screen] [instant wavy pixels somewhere on the screen] [instant no signal black screen] [normal screen]. **To Reproduce** Steps to reproduce the behavior, like: 1. Connect to pikvm (from internal or external network, doesn't matter, the issue occurs in both). 2. Stay connected and use it for few hours. **Expected behavior** Being able to stay connected and use it for few hours without any random instant GFX issues (wavy pixels) which occasionally followed by instant No Signal black screen interruptions assuming stable internet connection. **Actual behavior** Random instant GFX issues (wavy pixels) which occasionally followed by instant No Signal black screen starts appearing after some time (could be after minutes or hours) where it works fine until that point. It could happen again randomly after some time (could be minutes or hours). Note that I had sessions where the issue could get so severe it would be happening like every 15-30seconds (which is not that random anymore). These are my runtime settings: <img width="394" alt="runtime settings" src="https://github.com/pikvm/pikvm/assets/134864072/f37a3cde-90f9-452b-bbb7-cff5d9669ed3"> **Some discord channel members said about this issue** "if it goes to uncanny valley, it's the encoder on the pi, not sure why but it is. and I've seen that kind of behavior before." "I wouldn't think the signals would get wavy there because it's digital until it gets to the Toshiba chip but it is parallel digital signals..." "it's a digital signal, like packets over an ethernet cable, if there's disturbance the internet doesn't get wavy" "the Pi does signal processing on the images coming in " "It's kind of artistic, though I agree it's not the expected look." "no signal processing should occur until it reaches the decoder chip on the Pi 4. In theory at least." **Including support members said about this issue** "we have seen some odd behavior from port expanders" "no signal is the one I have seen and saw reported" "We have heard about odd behaviors from port expanders - mainly a No Signal as a result of pikvm not knowing what the target resolution is so it keeps trying different resolutions which would explain the random like No Signals you have seen" **Things I've tried to resolve the issue** - Change setting to gop 0 or play with kbps/bitrate. - switch hdmi cables (used both the hdmi cable that comes with pikvm from pi shops and amazon basics hdmi cable). - I thought initially that ezcoo is causing it, so I connected the pikvm directly to the adapter without ezcoo. - updated pikvm software to the latest version. - Made sure target machine advanced display settings it shows 1080p at 50 hz resolution. **Logs:** *I'll try to get the logs after the issue occurs next time to see if there is anything about it in the log that could be useful (or please let me know what kind of logs do you need). **Screenshots/Videos** This is what the gfx issue (wavy pixels) look like (note how towards the end of the video a large portion of the pixels are "melting" and going out of order): https://github.com/pikvm/pikvm/assets/134864072/9a289305-d8f5-4191-9803-fd0a75eb2d3c Wavy pixels: ![image](https://github.com/pikvm/pikvm/assets/134864072/2b31fce1-84aa-4d5f-8fa8-56553f87f2b5) ![image](https://github.com/pikvm/pikvm/assets/134864072/d8da8810-c495-41ad-8815-8d5d1175af09) Note that it's happening in different areas in different programs, windows, etc. It causes some letters sentences to tilt like a wave in some area / lines of the screen. And this is the regular display how it should be: ![image](https://github.com/pikvm/pikvm/assets/134864072/0affd406-87b3-4190-8f9c-9ef8a6d3088f) Occasionally it's followed by instant No Signal black screen (I found this picture on google images for illustration purposes, I believe the "no signal" letters are in yellow in the pikvm version): ![image](https://github.com/pikvm/pikvm/assets/134864072/978fb66f-67a1-40e1-8362-016b37b9025e) **Desktop (please complete the following information):** - OS: [e.g. iOS] Windows 11 - Browser [e.g. chrome, safari] Chrome 120.0.6099.225 (Official Build) (64-bit) (cohort: Stable) - Version [e.g. 22] - VNC client (if used) **PiKVM info:** - Raspberry Pi board version [e.g. RPi 4] PiKVM v3 Pre-Assembled - PiKVM platform [e.g. v2-hdmi] - Video capture type [e.g. CSI bridge] - KVMD version: `pacman -Q | grep kvmd` kvmd 3.293-1 kvmd-fan 0.29-1 kvmd-oled 0.26-1 kvmd-platform-v3-hdmi-rpi4 3.293-1 kvmd-webterm 0.48-1 - uStreamer version: `pacman -Q | grep ustreamer` ustreamer 5.48-2 - Linux kernel: `uname -a` Linux pikvm 6.1.61-1-rpi-ARCH #1 SMP Fri Nov 3 20:48:52 MSK 2023 armv7l GNU/Linux **Additional context** I tried to connect a physical Dell monitor to the MOKiN adapter hdmi port - And I haven't observed the reported issues happening. So what is it about the encoder on the pi that's randomly messing up the hdmi transmission causing instant wavy pixels and/or no signal black screen - I don't think the adapter used should affect how pikvm shows the signal (especially if the adapter works fine with a physical monitor). Note: I have two PiKVMs and it happened with both.

deekerman

2026-02-20 14:06:50 -05:00

closed this issue
added the
resolution:fixed

type:question
labels

deekerman commented

2026-02-20 14:06:51 -05:00

Author

Owner

@plia7 commented on GitHub (Jan 22, 2024):

@Amt921 Just for reference, you mentioned for this issue on 01/18/2024 that "we will see what we can do".

@plia7 commented on GitHub (Jan 22, 2024): @Amt921 Just for reference, you mentioned for this issue on 01/18/2024 that "we will see what we can do".

deekerman commented

2026-02-20 14:06:52 -05:00

Author

Owner

@plia7 commented on GitHub (Jan 22, 2024):

@Amt921 As you asked, I tried to test this in MJPEG mode and was able to reproduce the wavy pixels issue (Some letters on a screen in an ide text editor started to wave, like some gfx noise was happening in that area middle of the screen), although it wasn't followed by a no signal black screen (maybe that could happen only in H.264 mode?).

Also I switched back to H.264, the gfx glitch just happened twice in a span of 7 seconds with 3 seconds each glitch (with 1 second break between them), it wasn’t followed by a no signal black screen, so maybe a no signal black screen is not always happening after the wavy pixels (might be a separate issue).

As mentioned, I'll be testing tomorrow with the physical display the entire day to confirm it doesn't happen there.

@plia7 commented on GitHub (Jan 22, 2024): @Amt921 As you asked, I tried to test this in MJPEG mode and was able to reproduce the wavy pixels issue (Some letters on a screen in an ide text editor started to wave, like some gfx noise was happening in that area middle of the screen), although it wasn't followed by a no signal black screen (maybe that could happen only in H.264 mode?). Also I switched back to H.264, the gfx glitch just happened twice in a span of 7 seconds with 3 seconds each glitch (with 1 second break between them), it wasn’t followed by a no signal black screen, so maybe a no signal black screen is not always happening after the wavy pixels (might be a separate issue). As mentioned, I'll be testing tomorrow with the physical display the entire day to confirm it doesn't happen there.

deekerman commented

2026-02-20 14:06:52 -05:00

Author

Owner

@plia7 commented on GitHub (Jan 24, 2024):

@Amt921 As discussed, I tested with the physical display the entire day today and I haven't seen the issue even once. Please see if you can reproduce the issue with the MOKiN adapter on your side. Thank you.

@plia7 commented on GitHub (Jan 24, 2024): @Amt921 As discussed, I tested with the physical display the entire day today and I haven't seen the issue even once. Please see if you can reproduce the issue with the MOKiN adapter on your side. Thank you.

deekerman commented

2026-02-20 14:06:52 -05:00

Author

Owner

@plia7 commented on GitHub (Jan 24, 2024):

@Amt921 I take it back, I just saw the wavy pixels issue with the physical monitor. I’m closing the ticket. It happened in the physical monitor with both just wavy pixels and also wavy pixels followed by a black screen. So I’m guessing it’s coming from the adapter, I’ll have to try the dell adapter again to see if it doesn’t happen there or if it’s a deeper issue than that (or maybe same adapter on a different pc). Thanks again for your help.

@plia7 commented on GitHub (Jan 24, 2024): @Amt921 I take it back, I just saw the wavy pixels issue with the physical monitor. I’m closing the ticket. It happened in the physical monitor with both just wavy pixels and also wavy pixels followed by a black screen. So I’m guessing it’s coming from the adapter, I’ll have to try the dell adapter again to see if it doesn’t happen there or if it’s a deeper issue than that (or maybe same adapter on a different pc). Thanks again for your help.