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Groups > comp.os.linux.misc > #7642

Re: assigning specific /dev/videoN to specific USB webcams

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On Sunday, March 24th, 2013, at 21:51:32h +0000, Kevin Snodgrass explained:

> I have 2 DVRs, 1 has 2 identical Hauppauge PVR-250 cards, but they are 
> just straight NTSC cable

Not changed to digital (as in digital cable) yet?

> So far, the webcam always seems to be /dev/video0, but the PVR-250 and
> the pcHDTV seem to be randomly assigned /dev/video1 and /dev/video2

Well probably because the kernel is probing the USB ports before
it gets on to the PCI slots where the cards are located.

Your problem is rather more difficult to resolve because both
of your cards are the same model.  Theoretically it should be
possible to create a udev rule based on the absolute pci_path_to_device
string because they are in different slots.

> BTW, does anyone know why the pcHDTV 3000 does NOT use /dev/videoX ?  It 
> uses /dev/dvb/adapterX/dvrX.  Is there a techinical reason why the device 
> driver authors chose that instead of /dev/videoX ?

Well the explanation for that is not too difficult, but I can only give
it in general terms.  Your analog cards are assigned /dev/videoN device
ids (as is the case for webcams) by the appropriate video4linux v4l2 kernel
module whereas for DVB devices, the appropriate video4linux DVB modules
create a directory adapter under which there are device files for each of
the capabilities of the card, eg for a Terratec Cinergy 1200 DVB-t

ll /dev/dvb/adapter0/
total 0
0 drwxr-xr-x 2 root root     140 2013-03-24 21:03 ./
0 drwxr-xr-x 3 root root      60 2013-03-24 21:03 ../
0 crw-rw---- 1 root video 212, 4 2013-03-24 21:03 ca0
0 crw-rw---- 1 root video 212, 0 2013-03-24 21:03 demux0
0 crw-rw---- 1 root video 212, 1 2013-03-24 21:03 dvr0
0 crw-rw---- 1 root video 212, 3 2013-03-24 21:03 frontend0
0 crw-rw---- 1 root video 212, 2 2013-03-24 21:03 net0

So oversimplifying perhaps -- analog video devices
use /dev/videoN files, whereas digital video devices use
/dev/dvb/adapterN directories.


But back on the topic of udev rules, it seems that this is not the
newgroup that has any udev gurus.

Can anybody suggest where is the best place to get some help?

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Thread

assigning specific /dev/videoN to specific USB webcams J G Miller <miller@yoyo.ORG> - 2013-03-17 19:20 +0000
  Re: assigning specific /dev/videoN to specific USB webcams Robert Heller <heller@deepsoft.com> - 2013-03-17 14:46 -0500
    Re: assigning specific /dev/videoN to specific USB webcams J G Miller <miller@yoyo.ORG> - 2013-03-17 20:04 +0000
  Re: assigning specific /dev/videoN to specific USB webcams Kevin Snodgrass <kdsnodgrass@yahoo.com> - 2013-03-24 21:51 +0000
    Re: assigning specific /dev/videoN to specific USB webcams J G Miller <miller@yoyo.ORG> - 2013-03-24 22:54 +0000
      Re: assigning specific /dev/videoN to specific USB webcams Robert Heller <heller@deepsoft.com> - 2013-03-24 18:27 -0500
        Re: assigning specific /dev/videoN to specific USB webcams J G Miller <miller@yoyo.ORG> - 2013-03-25 02:34 +0000
      Re: assigning specific /dev/videoN to specific USB webcams Kevin Snodgrass <kdsnodgrass@yahoo.com> - 2013-03-31 18:16 +0000
        Re: assigning specific /dev/videoN to specific USB webcams J G Miller <miller@yoyo.ORG> - 2013-03-31 19:33 +0000
          Re: assigning specific /dev/videoN to specific USB webcams Kevin Snodgrass <kdsnodgrass@yahoo.com> - 2013-04-11 14:19 +0000
            Re: assigning specific /dev/videoN to specific USB webcams J G Miller <miller@yoyo.ORG> - 2013-04-11 15:21 +0000
  Re: assigning specific /dev/videoN to specific USB webcams Eric Pozharski <whynot@pozharski.name> - 2013-04-01 13:52 +0300
    Re: assigning specific /dev/videoN to specific USB webcams J G Miller <miller@yoyo.ORG> - 2013-04-01 18:24 +0000

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