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ubuntu v4lv2 webcam cvCaptureFromCAM returns NULL

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ubuntu v4lv2 webcam cvCaptureFromCAM returns NULL

miasmaktoday
I got the openCV libraries from the svn repositories and built them. I used the latest_tested_snapshot on 7 march 2009. Compile and build and install went fine as did building of the samples and running the tests as explained in the wiki. I did not change any of the build settings.

However I can't seem to get any of the samples, which require a webcam, working. The samples work with .avi files or .jpg files.

I made a C project in eclipse and started debugging and I find that the pointer returned from cvCaptureFromCAM returns a NULL. I tried passing -1 and 0 as parameter to cvCaptureFromCAM. My video camera is accessible from /dev/video0/

I also tried a python example found at http://linux.softpedia.com/progDownload/WebcamDemo-Download-42417.html
with the same results, the equivalent of cvCaptureFromCAM returns a null.

If I run gstreamer-properties and I choose v4lv2 in the Video tab and I test it, it works correctly visually but gives an error code libv4lconvert: Error decompressing JPEG: unknown huffman code: 0000ffff

Also cheese and xawtv work.

I am using ubuntu 8.10.
uname -a says:
Linux rala 2.6.27-11-generic #1 SMP Thu Jan 29 19:24:39 UTC 2009 i686 GNU/Linux

Any clues/things to try/search terms for google would be greatly appreciated?


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Re: ubuntu v4lv2 webcam cvCaptureFromCAM returns NULL

Alejandro Weinstein
On Tue, Mar 17, 2009 at 1:00 PM, miasmaktoday <[hidden email]> wrote:
> However I can't seem to get any of the samples, which require a webcam, working. The samples work with .avi files or .jpg files.

Check these bugs:
https://bugs.launchpad.net/ubuntu/+source/opencv/+bug/321358
https://bugs.launchpad.net/opencvlib/+bug/260918
http://sourceforge.net/tracker/index.php?func=detail&aid=2653321&group_id=22870&atid=376677

Alejandro.
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Re: ubuntu v4lv2 webcam cvCaptureFromCAM returns NULL

miasmaktoday
In reply to this post by miasmaktoday
It seems there is a regression bug on Ubuntu that involves the v4l libraries. I can now get the sample code to work using something like
LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so ./facedetect

Here is the bug listing for OpenCV:
http://sourceforge.net/tracker/index.php?func=detail&aid=2653321&group_id=22870&atid=376677

Here is the bug tracked in launchpad:
https://bugs.launchpad.net/ubuntu/+source/libv4l/+bug/260918

So I am up and running!

In Eclipse I just configured the debug configuration to have an environment variable LD_PRELOAD with value /usr/lib/libv4l/v4l1compat.so

--- In [hidden email], "miasmaktoday" <maiatoday@...> wrote:

> However I can't seem to get any of the samples, which require a webcam, working. The samples work with .avi files or .jpg files.
>
> I made a C project in eclipse and started debugging and I find that the pointer returned from cvCaptureFromCAM returns a NULL. I tried passing -1 and 0 as parameter to cvCaptureFromCAM. My video camera is accessible from /dev/video0/
>
> I also tried a python example found at http://linux.softpedia.com/progDownload/WebcamDemo-Download-42417.html
> with the same results, the equivalent of cvCaptureFromCAM returns a null.
>
> If I run gstreamer-properties and I choose v4lv2 in the Video tab and I test it, it works correctly visually but gives an error code libv4lconvert: Error decompressing JPEG: unknown huffman code: 0000ffff
>
> Also cheese and xawtv work.
>
> I am using ubuntu 8.10.




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Re: ubuntu v4lv2 webcam cvCaptureFromCAM returns NULL

Ang Chee Beng
Hi,

I couldn't find /usr/lib/libv4l/v4l1compat.so. In fact, I couldn't find any v4lcompat.so file anywhere. I do find /lib/modules/2.6.24-16-generic/kernel/drivers/media/video/v4l1-compat.ko in my ubuntu.

Did I do anything wrong with the setup?

Can anyone help, please?

Thanks.
Ang

--- In [hidden email], "miasmaktoday" <maiatoday@...> wrote:

>
> It seems there is a regression bug on Ubuntu that involves the v4l libraries. I can now get the sample code to work using something like
> LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so ./facedetect
>
> Here is the bug listing for OpenCV:
> http://sourceforge.net/tracker/index.php?func=detail&aid=2653321&group_id=22870&atid=376677
>
> Here is the bug tracked in launchpad:
> https://bugs.launchpad.net/ubuntu/+source/libv4l/+bug/260918
>
> So I am up and running!
>
> In Eclipse I just configured the debug configuration to have an environment variable LD_PRELOAD with value /usr/lib/libv4l/v4l1compat.so
>
> --- In [hidden email], "miasmaktoday" <maiatoday@> wrote:
>
> > However I can't seem to get any of the samples, which require a webcam, working. The samples work with .avi files or .jpg files.
> >
> > I made a C project in eclipse and started debugging and I find that the pointer returned from cvCaptureFromCAM returns a NULL. I tried passing -1 and 0 as parameter to cvCaptureFromCAM. My video camera is accessible from /dev/video0/
> >
> > I also tried a python example found at http://linux.softpedia.com/progDownload/WebcamDemo-Download-42417.html
> > with the same results, the equivalent of cvCaptureFromCAM returns a null.
> >
> > If I run gstreamer-properties and I choose v4lv2 in the Video tab and I test it, it works correctly visually but gives an error code libv4lconvert: Error decompressing JPEG: unknown huffman code: 0000ffff
> >
> > Also cheese and xawtv work.
> >
> > I am using ubuntu 8.10.
>


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Re: ubuntu v4lv2 webcam cvCaptureFromCAM returns NULL

Morgan-2
In reply to this post by miasmaktoday

> It seems there is a regression bug on Ubuntu that involves the v4l libraries. I can now get the sample code to work using something like
> LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so ./facedetect


I'm experiencing problems with my camera too. While Cheese and xwatv work perfectly, camorama and opencv don't. If I preload v4l like you, I only see some kind of corrupted image (that's with a Logitech Orbicam and a Logitech Quickcam Chat).

In gstreamer-properties, I get the same corrupted image if I test video4linux 1. But it works perfectly with video4linux 2! I tried preloading v4l2convert.so without success.

Does anyone know how to force OpenCv to work with whatever Chesse uses, or video4linux2?

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Re: ubuntu v4lv2 webcam cvCaptureFromCAM returns NULL

naveen143
This post has NOT been accepted by the mailing list yet.
In reply to this post by miasmaktoday
Hi I am doing project in wireless sensor networks using python coding language and in that process I need to access a webcam using v4l2 and I am need of that code as I need to submit it by tomarrow.I would be thankful if you help me in this.
Thanks
Naveen


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