Video v-flipping/flickering problem

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Video v-flipping/flickering problem

Postby a.terenzi » Mon Sep 10, 2007 9:18 am

I noticed that the video from the webcam sometimes flickers and is not very smooth anyway... it looks like that, when the video flickers, the video is displayed upside down for a while...

I realized about this behaviour because when I hit ESC the video freezes on the last frame before exiting...

I'm not sure, but this behaviour seems due to something strange in flushing the framebuffer in the wrong moment... I suppose that, maybe, the video is originally vertically flipped and it shows up from time to time in some frames... is there a way to solve this problem?

Thanks. Best regards.

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Postby a.terenzi » Tue Sep 11, 2007 6:44 am

I'm investigating the problem... I noticed that using the not v-flipped version of camera's configuration (WDM_camera.xml) the video is smooth and doesn't flickers at all... so I guess that there is something strange in the code that flips the video before flushing the frame buffer... I need to try to fix it and I'm thinking about 2 ways to do it:

1. modify osgART to map in a different way the video plane...(but this is just an idea since I don't know how everything is implemented yet...)

2. modify the my scene graph to transform the video plane in my scene... but I don't know if it is an easy task since the reference frame for the video background is set to ABSOLUTE, I guess, so if I don't mistake, I will not be able to transform it...

...any suggestion?
Thanks. Regards.

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Postby retrakker » Wed Sep 12, 2007 8:56 pm

Sometimes this behaviour can be replicated with the DSVL or ARToolKit videotest example. Usually it is due to drivers, but you are also right there is some dodgy flipping code in DSVL which might contribute to this behaviour.


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Postby a.terenzi » Wed Sep 12, 2007 11:58 pm

I managed to solve the problem in the following way:

1. I modified little code of osgART in order to be able to change the reference frame of the videobackground from ABSOLUTE to RELATIVE

2. in my scene graph I added a MatrixTransform above my video background node in order to scale 'y' by -1 (v-flip)

3. I set the added MatrixTransform node's reference frame to ABSOLUTE

In this way the video stream is perfect :) smoother and no flickering at all.

Talking about the changes I made in osgART, I just added a method to get the modelview matrix of the video background and changed from 'private' to 'protected' the modelview member of VideoLayer.

Waiting for new release of osgART, I'd like to suggest to add a new feature to the new release: i.e. the possibility to have a MatrixTransfrom (like the one I used) to allow some 2D transfroms, like flippings and translations, on video backgrounds...

Thank. Best regards.

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I second that

Postby tomhog » Fri Sep 14, 2007 2:59 am

I've had to make the same kind of modifications

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Postby julian » Fri Sep 14, 2007 1:02 pm

I understand the problem here is that you need to flip the video, but DSVL (or something in there) is having issues that make it flicker. However, I don't think simply flipping the image when you display it will work...

It's possible that if the video coming into your application is not flipped the right way, whichever tracker you are using is not going to be able to track markers correctly.

Even if it did, if you flip the video background using a matrix transform, then the 3D objects you draw in front of the video background will no longer be aligned with the markers in the video. You would need to flip everything.

I think the problem needs to be resolved at the source (DSVL) or at the video plugin level, not at the renderer level.

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Re: Video v-flipping/flickering problem

Postby Kabal2013 » Thu Feb 04, 2010 8:33 am

I've the same issues of video flickering, only video, not 3d rendered objects.
I've noticed that I don't have technical issues about flickering if I use Artoolkit HertmutPre 2.8 + OSG 2.8.2 + OSGArt 2.0 RC3; but if I use OSG 2.9.6 the problem appear again. So I think is inside the 2.9.6, but will be useful for me to use this last version.

Are there rumors about a fix?


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Re: Video v-flipping/flickering problem

Postby Laura50 » Sun Feb 20, 2011 6:46 pm

I don't understand why someone can't make an affordable web cam that doesn't flicker or stall. The one I have now has very poor quality, not sure if it has anything to do with the cables I'm using.

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Joined: Mon Oct 31, 2011 6:22 am

Re: Video v-flipping/flickering problem

Postby marjorie100 » Mon Oct 31, 2011 6:26 am

I have the Pinnacle card and I've tried everything I can to eliminate the flicker when exporting to tape. But I've been facing this problem for such a long time. I normally save my project settings as No Fields and put the flicker removal to the slow texas Hold Em Tex motion and still clips, but it isn't working. Please, in case ayone has a suggestion, I woulb be glad to know about it.

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