[Linux-uvc-devel] Two webcams simultaneously on the same USB

Paulo Assis pj.assis at gmail.com
Fri May 29 23:40:58 CEST 2009


Javier,
I've done some more testing and this is what I found when capturing
640x480 at 25fps video from 2 uvc cameras on the same controler, both from
logitech a QC5000pro and another camera I've been testing:
- I can capture video from both of them when streaming MJPEG data on the two
cameras.
- I can capture video from both of them when streaming MJPEG data from one
and YUYV data from the other one.
- when using a YUYV stream on both I can only capture from the first camera,
from the second I get a error of no space left, basically the USB bandwith
is not enought.

Best regards,
Paulo

2009/5/29 Javier Martinez Baena <jbaena at decsai.ugr.es>

>
> Thanks Paulo, not only Logitech fails, but also Creative (Optia AF at
> least).
> I will get a new Philips soon ... I hope this will work better.
>
>
> On Fri, 29 May 2009 13:49:55 +0100, Paulo Assis wrote
> > Javier Hi,
> > You should know that at least logitech cameras don't handle well usb
> > hubs, logitech is very clear on this, if you want you can get more
> > info on the quickcamteam site and forums, it has something to do
> > with the way data is handled by most usb hubs. Anyway I have been
> > able to connect up to 3 uvc cameras simultaneously in my pc, and I
> > believe two of them were on the same host (I mounted the pc myself
> > so I should know this for sure, but my memory has seen better days :)
> >  ), all of them use the ehci driver. Some drivers are in fact buggy,
> > just check the following link for a example
> > (in this case the musb driver):
> http://forums.quickcamteam.net/showthread.php?tid=821
> >
> > Best regards,
> > Paulo
> >
> > 2009/5/29 Javier Martínez Baena <jbaena at decsai.ugr.es>
> >
> > > >Hi Javier,
> > > >
> > > >On Friday 22 May 2009 09:36:32 J. Martínez Baena wrote:
> > > >> Hello,
> > > >
> > > >> I have a problem with 2 webcams I'm trying to get work
> simultaneously. I
> > > >> have several models (Logitech P3000, Logitech P9000, Creative
> LiveCAM
> > > Optia
> > > >> AF, Philips). When I plug two of them on different USB ports, then
> > > >> everything works ok: I can see both simultaneously with, for
> example,
> > > >> luvcview.
> > > >>
> > > >> The problem exists when I plug two of them on the same USB (for
> example
> > > on
> > > >> frontal USB or in a USB hub). I've got the problem for combinations
> in
> > > wich
> > > >> UVC driver is used by both cameras. I can get frames for one of them
> > > (the
> > > >> first that I try), but for the second one I get a "noisy/green"
> screen
> > > ...
> > > >> it seems as if the image is corrupted.
> > > >>
> > > >> However, if I put the philips and the logitech P9000/Optia it works
> > > fine.
> > > >> The Philips (and logitech P3000) use a different driver than UVC.
> Also,
> > > I
> > > >> can plug two philips webcam and they works fine.
> > > >>
> > > >> ¿Is this a bug or an unresolved problem of the UVC driver? ¿Is it a
> USB
> > > >> problem?
> > > >
> > > >My guess is that you're having USB bandwidth issues. As the uvcvideo
> > > driver
> > > >starts capturing video on both cameras, you're not exceeding the
> > > theoretical
> > > >USB bandwidth limit. However, bugs in the USB host controller, the USB
> > > host
> > > >controller driver or the camera can result in corrupted data. Could
> you
> > > >perform the same test on another computer ?
> > > >
> > > >Best regards,
> > > >
> > > >Laurent Pinchart
> > >
> > >
> > > Hi Laurent,
> > >
> > > Sorry for the delay ... I make some tests on several computers and the
> > > problem
> > > persists. My guess is that is a problem of UVC driver (but I'm not an
> > > expert
> > > ... so it's only a guess!). When I connect different webcams (using
> other
> > > driver than UVC) it works.
> > >
> > > I tried with different resolutions (320x240, 640x480, ...) and
> different
> > > framerates.
> > >
> > > Sometimes, when a cam is running (capturing), I can't even initialice
> the
> > > other one (neither consult for allowed resolutions, etc).
> > >
> > > But I don't know how USB driver works, so, maybe an USB problem.
> > >
> > > Best regards
> > >
> > >
> > > _______________________________________________
> > > Linux-uvc-devel mailing list
> > > Linux-uvc-devel at lists.berlios.de
> > > https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
> > >
>
>
> --
> Dr. Javier Martínez Baena
> Dpto. Ciencias de la Computación e I. A.
> E.T.S. de Ingeniería Informática
> Universidad de Granada
> Tlf: 958 240802
> Fax: 958 243317
> Email: jbaena at decsai.ugr.es
>
> --
> DEpartment of Computer Science and A.I. http://decsai.ugr.es
>
>
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