How to selecting a video4linux camera based on its serial number from gst-launch?

[James Linder]

> On Mar 1, 2024, at 03:39, Henning Larsen via gstreamer-devel <gstreamer-devel at lists.freedesktop.org> wrote:
> 
> A command like this launches /dev/video0
> gst-launch-1.0 -v v4l2src device=/dev/video0 ! videoconvert ! autovideosink
> But when you have multiple cameras and they are enumerated in a random order you usually need to be able to identify each camera on - say its serial number.
> 
> It is easy to find the serial number including many other properties using the command
> $udevadm info /dev/video0
> The serial number for example, would be called 
> ID_SERIAL_SHORT=12345
> 
> How to use this serial number in the gst-launch string instead of the /dev/videoX id?
> 
> I tried 
> gst-launch-1.0 -v v4l2src device=$(python find_camera_by_sn.py 12345) ! videoconvert ! autovideosink
> And it works - inside a shell, but not inside a MediaMTX.yml configuration file, and I need it to work there. I suspect it is because it does not support the shell command. In any case it is not an elegant method - better to stick with what is provided by gstreamer - if possible.
> 
> I would think this must be a fairly common issue so does there exist a plugin/filter for gstreamer to achieve this device selection based on a specific property?

I’d totally isolate the problem by using udev to ensure camera A was always video0, B was (whatever is next ie video1, video4)
Then gstreamer always uses videoN

James

PS udev rules allow you to choose SN or Bus ID or ...