Cam Link 4K - was working, but now it isn't

20.04 on a Lenovo X1 carbon, if it matters

I have a Cam Link 4K USB HDMI adapter, the purpose of which is to connect the HDMI output of a camera to a USB input. I have managed to get it working in the past. However, I had to reboot today, and now, though I can get the device to work with cheese, it does not work with any of the meeting applications I use (zoom and ringcentral).

I have a locally-built version of the v42loopback module, and I've installed it with

modprobe v4l2loopback max_buffers=2 devices=1 exclusive_caps=1

My v42l-ctl output is:

% v4l2-ctl --list-devices
Dummy video device (0x0000) (platform:v4l2loopback-000): /dev/video0
Synaptics RMI4 Touch Sensor (rmi4:rmi4-00.fn54): /dev/v4l-touch0
Cam Link 4K: Cam Link 4K (usb-0000:00:14.0-1.2): /dev/video1 /dev/video2 /dev/media0

I then start ffmpeg:

ffmpeg -f v4l2 -framerate 50 -pix_fmt yuyv422 -video_size 1920x1080 -i /dev/video1 -f v4l2 -vcodec rawvideo -pix_fmt yuv420p /dev/video0

I don't completely understand what that means, but it has worked for me many times in the past. Now, when I try all this stuff, I can get my video input up on the screen via cheese. That is, I start cheese and it works; I see the video and it's obviously live.

However, unlike in the past, the video is unavailable in zoom or ringcentral; the applications simply do not allow video. I have no clue at all what could be going on, or even any way of diagnosing the issue; the video is simply not available.

What can I do to figure out what those applications need in order to get the video working again?

edit I do verify the device info when I start ffmpeg to make sure the device assignments are correct; the above v42l-ctl output is usually how things look, but for random reasons the devices are different sometimes.

1 Answer

Try running:

sudo usbreset "Cam Link 4K"

you may need to run "sudo apt install usbutils" to get the usbreset command.