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

Thu Feb 29 22:29:11 UTC 2024

Hej Peter, Hi Nicolas
Thank you so much for your swift replies.

I have only tested Peter's suggestion so far and it works nicely!

So to recap for other readers - the command used is
gst-launch-1.0 v4l2src
device=/dev/v4l/by-id/usb-FLIR_Boson_53112-video-index0 ! videoconvert !
autovideosink
where the device path obviously will vary on the last part.
It also works in the MediaMTX.yml context, albeit with an encoding element
downstream of the device.
The device string is unique for this camera - which is what I needed.

Again Thanks for your help - it is very appreciated!
I will investigate Nicolas' suggestion later.
br henning

I found a small heads-up:
Dont do
$cd /dev/v4l/
and investigate the devices while testing plugging and unplugging because
the folder gets deleted if there are no devices. The result is that the
shell $ls shows an empty folder.
So do $cd .. out and back in and it gets populated.
Bottom line - list devices from outside the folder and you'll be good

------------------------------
>
> Message: 2
> Date: Thu, 29 Feb 2024 21:58:31 +0100
> From: Peter Maersk-Moller <pmaersk at gmail.com>
> To: Discussion of the development of and with GStreamer
>         <gstreamer-devel at lists.freedesktop.org>
> Subject: Re: How to selecting a video4linux camera based on its serial
>         number from gst-launch?
> Message-ID:
>         <
> CAGf_jGnQ6sXm2Lpwp-HTXt8AfA2-OSyMjesX_9mGr9iu08fU2g at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi Henning.
>
> Try take a look into /dev/v4l/by-id/ directory. Maybe you can use the id
> there to obtain the functionality you want.
>
> Regards
> Peter Maersk-Moeller
>
> On Thu, Feb 29, 2024 at 8:39?PM 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
> > <https://github.com/bluenviron/mediamtx>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?*
> >
> > Any hints are appreciated.
> > Thanks
> > henning
> >
> >
> > *Should someone need it: This is the python code find_camera_by_sn.py*
> > import sys
> > import pyudev
> >
> > def find_camera_by_serial(serial):
> >     context = pyudev.Context()
> >     for device in context.list_devices(subsystem='video4linux'):
> >         if 'ID_SERIAL_SHORT' in device.properties:
> >             if device.properties['ID_SERIAL_SHORT'] == serial:
> >                 return device.device_node
> >     return None
> >
> > if __name__ == '__main__':
> >     # Example: Find camera with serial number 'ABC123'
> >     # manual command to list video4linux cameras
> >     # udevadm info /dev/video0,   etc for 0,1,,3
> >     default_dev = "/dev/video0"
> >     if len(sys.argv) == 2:
> >         camera_device = find_camera_by_serial(sys.argv[1])
> >         if camera_device:
> >             print(camera_device)
> >         else:
> >             print(default_dev)
> >     else:
> >         print(default_dev)
> >
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> ------------------------------
>
> Message: 3
> Date: Thu, 29 Feb 2024 16:10:22 -0500
> From: Nicolas Dufresne <nicolas at ndufresne.ca>
> To: Discussion of the development of and with GStreamer
>         <gstreamer-devel at lists.freedesktop.org>
> Cc: Henning Larsen <henning.e.larsen at gmail.com>
> Subject: Re: How to selecting a video4linux camera based on its serial
>         number from gst-launch?
> Message-ID:
>         <3490e94f2d7bb015e9559e1eed676d368263fed4.camel at ndufresne.ca>
> Content-Type: text/plain; charset="utf-8"
>
> Hi,
>
> Le jeudi 29 f?vrier 2024 ? 20:39 +0100, Henning Larsen via gstreamer-devel
> a
> ?crit?:
> > 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
>
> In the UVC space, were cheap Chinese market too over, you'll quickly find
> that
> serial number can be unreliable. You may have 0, or the same serial for
> all cams
> of the same model/brand. libcamera made up a proper ID generator, though
> it will
> change if you change the actual USB port.
>
> > How to use this serial number in the gst-launch string instead of the
> > /dev/videoX id?
>
> Its not support directly. Instead, we offer a tool (for software to use)
> that is
> called GstDeviceMonitor, and V4L2 plugin offer a matching DeviceProvider.
> There
> is a command line to excersize that tool:
>
> gst-device-monitor-1.0 Video/Source
> Device found:
>
> name : Integrated Camera: Integrated C
> class : Video/Source
> caps : video/x-raw, format=YUY2, width=1280, height=720,
> pixel-aspect-ratio=1/1,
> framerate=10/1
> video/x-raw, format=YUY2, width=960, height=540, pixel-aspect-ratio=1/1,
> framerate=15/1
> video/x-raw, format=YUY2, width=848, height=480, pixel-aspect-ratio=1/1,
> framerate=20/1
> video/x-raw, format=YUY2, width=640, height=480, pixel-aspect-ratio=1/1,
> framerate=30/1
> video/x-raw, format=YUY2, width=640, height=360, pixel-aspect-ratio=1/1,
> framerate=30/1
> video/x-raw, format=YUY2, width=424, height=240, pixel-aspect-ratio=1/1,
> framerate=30/1
> video/x-raw, format=YUY2, width=352, height=288, pixel-aspect-ratio=1/1,
> framerate=30/1
> video/x-raw, format=YUY2, width=320, height=240, pixel-aspect-ratio=1/1,
> framerate=30/1
> video/x-raw, format=YUY2, width=320, height=180, pixel-aspect-ratio=1/1,
> framerate=30/1
> image/jpeg, parsed=true, width=1280, height=720, pixel-aspect-ratio=1/1,
> framerate=30/1
> image/jpeg, parsed=true, width=960, height=540, pixel-aspect-ratio=1/1,
> framerate=30/1
> image/jpeg, parsed=true, width=848, height=480, pixel-aspect-ratio=1/1,
> framerate=30/1
> image/jpeg, parsed=true, width=640, height=480, pixel-aspect-ratio=1/1,
> framerate=30/1
> image/jpeg, parsed=true, width=640, height=360, pixel-aspect-ratio=1/1,
> framerate=30/1
> image/jpeg, parsed=true, width=424, height=240, pixel-aspect-ratio=1/1,
> framerate=30/1
> image/jpeg, parsed=true, width=352, height=288, pixel-aspect-ratio=1/1,
> framerate=30/1
> image/jpeg, parsed=true, width=320, height=240, pixel-aspect-ratio=1/1,
> framerate=30/1
> image/jpeg, parsed=true, width=320, height=180, pixel-aspect-ratio=1/1,
> framerate=30/1
> properties:
> udev-probed = true
> device.bus_path = pci-0000:05:00.4-usb-0:2.1:1.0
> sysfs.path =
> /sys/devices/pci0000:00/0000:00:08.1/0000:05:00.4/usb4/4-2/4-2.1/4-
> 2.1:1.0/video4linux/video0
> device.bus = usb
> device.subsystem = video4linux
> device.vendor.id = 04ca
> device.vendor.name = 8SSC20F27068L1GZ9AN7T85
> device.product.id = 7070
> device.product.name = Integrated Camera: Integrated C
> device.serial = 8SSC20F27068L1GZ9AN7T85_Integrated_Camera
> device.capabilities = :capture:
> device.api = v4l2
> device.path = /dev/video0
> v4l2.device.driver = uvcvideo
> v4l2.device.card = Integrated Camera: Integrated C
> v4l2.device.bus_info = usb-0000:05:00.4-2.1
> v4l2.device.version = 395013 (0x00060705)
> v4l2.device.capabilities = 2225078273 (0x84a00001)
> v4l2.device.device_caps = 69206017 (0x04200001)
> gst-launch-1.0 v4l2src ! ...
>
>
> When programming the returned Device, can be use to create and configure
> the
> source element correctly, without having to know about the device
> property. You
> can see that it also provides bunch of information imported from udev,
> including
> the serial number if that is what you want to use. An alternative is to
> install
> libcamera with the gstreamer element, in there the camera names are unique
> and
> reusable. The other options is to create udev rules that alias you camera
> device
> names to a unique name instead of the auto-generated one.
>
> Nicolas
>
>
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