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http://bugs.kde.org/show_bug.cgi?id=124530
------- Additional Comments From taupter gmail com 2006-03-30 13:15 -------
Hello, Ingmar.
The insteresting thing is the device detection method resports your webcam as
having a max resolution of 640x480 and min of 160x120 and reports no error when
setting the video mode to 320x240 under V4L. Under V4L2 it reports as having a
max res of 32767x32767 and min res of 1x1 (pretty bogus values) and returns an
EINVAL (22) when setting the resolution to 320x240, but despite it the res and
colorspace read from the cam seems to be correct (Returned width: Planar YUV
4:2:0 320x240).
According to the image (attachment id=15362) the grabbed frame is 320x240 but
from the middle of a bigger 640x480 image handled internally by the camera
(similar to what a Genius webcam I own do _under_Windows_). I'm assuming your
device characteristics are those reported by the V4L driver (those make more
sense) and that the V4L2 support is not complete.
USB webcams cannot do mmap, so it uses "read" mode. If an error occurs when
reading it can be related to:
- Problems with conflicting irqs (I had this kind of problem in a Creative
Lab's webcam I own);
- Problems setting the correct colorspace (if your cam doesn't support RGB24 or
YUV420P format, but it seems to support according to the V4L values)
- ov511 driver may be broken for your specific webcam. A way to check it is to
try to use another video program and check if it correctly grabs frames and how
it behaves when you force a 320x240 resolution (in XawTV it can be done just
resizing the video window);
- A bug in Kopete's VideoDevice's code we should address.
About the 320x240 image geometry, it's the resolution used by both MSN and
Yahoo!, so it was chosen as a default, but it can be overriden by the
protocol's maintainer, but as the limitation is bound to those protocols
themselves, changinf this default resolution would not make too much sense,
because to use a 640x480 image under such protocols would infolve a resize
operation done by software to accomodate the captured frame to protocols'
constraints, rendering all this conversion proccess unuseful and harmful, as
the resizing operation would impact negatively performance and the end result
(both visually-wise and protocol-wise) would be the same as using the default
320x240 (QVGA) resolution. Using this resize scheme would make sense only if
the given webcam's hardware _cannot_ support QVGA resolution (a very rare case.
I never saw a single video device, be it a webcam or a capture card that cannot
support QVGA natively but supports VGA resolution. The only hardware I ever saw
that couldn't support QVGA at all was the 1st Creative Lab's webcam model that
should be plugged to the parallel port, circa 1997, that couldn't do anything
bigger than SQCGA (160x120)).
For now I'm assuming it's a problem with the ov511 driver, but the
aforementioned feedback about how your webcam behaves under another software
(e.g. XawTV) would do a lot to clarify the issue.
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