rationalsa
a46a886744
* return the first format reported rather than hardcoding YUYV - it seems to use NV12 for 4K capture * looser name match - it's reported as 'Cam Link 4K', not 'Cam Link 4K: Cam Link 4K' on my machine * check that the QUERYCAP is for V4L2_BUF_TYPE_VIDEO_CAPTURE * don't cache a device file descriptor * simplify the code
Camlink
A small library to force removal of invalid colorspaces exported by the Elgato Cam Link 4K.
Table of Contents
Setup
Prerequisites
You will need gcc and make to build.
Building
Run mkdir build && make
Installing
Simply run sudo make install. The camlink.so file will be copied to the path /usr/local/lib/camlink/camlink.so
Uninstalling
Run sudo make uninstall.
Usage
This library is run as a LD_PRELOAD to other applications. It intercepts all ioctl calls
and determines if the call is intended to query the colorspaces available on a camlink.
If so, it rejects all return values that are NOT YUYV 4:2:2. This should make colors work
correctly on the Camlink in Linux.
Examples
Video4Linux2 CTL application:
$ LD_PRELOAD=/usr/local/lib/camlink/camlink.so v4l2-ctl -d /dev/video2 --list-formats-ext
Zoom
$ LD_PRELOAD=/usr/local/lib/camlink/camlink.so zoom
Flatpak Zoom
$ flatpak override us.zoom.Zoom --filesystem=/usr/local/lib/camlink/camlink.so
$ flatpak run --env=LD_PRELOAD=/usr/local/lib/camlink/camlink.so us.zoom.Zoom
Firefox
$ LD_PRELOAD=/usr/local/lib/camlink/camlink.so firefox
Universal
export LD_PRELOAD=/usr/local/lib/camlink/camlink.so
Getting this to work in a desktop environment
Say you use Google Chrome. You click on the icon in your desktop environment, and it locates the .desktop file. (located @ /usr/share/applications/google-chrome.desktop on my machine)
Inside that file is an Exec= line that specifies how to the browser should be started. On my machine, the line is:
Exec=/usr/bin/google-chrome-stable %U
You need to edit that line, and you need that line to STAY edited even if you update Google Chrome. The solution is to make a local copy of this file in your home directory:
$ cp /usr/share/applications/google-chrome.desktop ~/.local/share/applications/
Then edit the new file @ ~/.local/share/applications/google-chrome.desktop and change the exec line to include the LD_PRELOAD call. Something like this:
Exec=env LD_PRELOAD=/usr/local/lib/camlink/camlink.so /usr/bin/google-chrome-stable %U
Troubleshooting
If running the browser on the command line DOES NOT WORK -- even after fully quitting it first:
Then the issue is different; likely the LD_PRELOAD path is incorrect. The examples assume that you have installed the camlink library. If you have not, instead use the path where your camlink.so file can be found. For example: LD_PRELOAD=/home/yourname/path/to/camlink/sources/build/camlink.so
This is a Cam Link 4K bug. What does Elgato support say?
I contacted Elgato about the issue and got this reply:
Thank you for contacting Elgato Technical support.
I understand you are in need of some information regarding running a Cam Link 4K on a Linux computer. I will be happy to help!
As it turns out, Linux OS is not supported. Elgato products were designed to work with Windows and Mac only.
I understand this may not be the information your were expecting to hear and for that I apologize.
So they will not be helpful. That doesn't mean you shouldn't contact them about the issue! Manufacterers need to know how their product is being used.
Alternatives
There are several other possible fixes for the color issue for the Cam Link 4K:
- Hack the firmware to stop returning invalid colorspaces
- Use a dummy video source and ffmpeg to convert the color to something different
- Build an exception into the v4l2 driver for the Camlink to ignore the extra colorspaces