[mythtv-users] Symptom?

Michael T. Dean mtdean at thirdcontact.com
Fri Aug 5 17:29:34 UTC 2005

Paul McKellar wrote:

>On 8/5/05, Marty Ravell <mythtv at rave-tech.com.au> wrote:
>>I've noticed that I only have a single device showing for 'll /dev/video?'.
>>i.e. /dev/video0
>>Is this normal? Jarod;s guide and various other sources seem to suggest that
>>there should be several video devices?
>>The system is PVR-350, P4, Intel Board, FC3, Jarod's guide. TV-out via the
>that is normal enough.  depending on what you use for a device system.
> udev or devfs or however you have them set up.  you only need one for
>each device, and often enough the additional ones people have aren't
>actually linked to anything substantive.
>i still feel like a newbie but that is what i've gathered.  hope it helps.
That's true, but the PVR-350 actually has several devices.  There's the 
encoding capture device (/dev/video0), the decoder output device 
(/dev/video16), the raw audio capture device (/dev/video24), the raw 
video capture device (/dev/video32), and the raw video display device 
(/dev/video48).  In addition, there's the radio tuner device 
(/dev/radio0), the vertical blank interval (CC/Teletext/WSS/etc) capture 
device (/dev/vbi0), the procesed vbi device (/dev/vbi4), the vbi display 
device (/dev/vbi8), and the framebuffer device /dev/fbX (where X is may 
vary depending on whether you have other framebuffers in the 
system--i.e. through the video card).

However, not having these other device nodes will not cause any 
problems--it only means you can't access those devices.  So, the lack 
of, for example, a raw video capture device node is probably not a 
concern for anyone.

How do you get the device nodes?  The right answer is to update/modify 
your udev scripts (I'm pretty sure FC3 is running Linux 2.6 and using 
udev for device node creation).  However, there are many other 
approaches (such as putting the appropriate mknod command in your 
startup scripts) for those who don't care whether it's right and don't 
care to learn how udev works (although, I've got to say, you won't 
appreciate the beauty of udev until you've learned how it works :).

Note, also, that some distros use scripts that create the video devices 
in places like /dev/v4l or /dev/video4linux or ... --and often with a 
link using a more "traditional" device name (like /dev/video0) (So, they 
may be there--just not where you're looking.)


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